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Genetics

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Heredity and Variation:

An organism produces an organism of similar kind. A pea plant give rise the seeds of pea, an apple seed produce apple tree and rice plant produce rice grains. Now there arise a question that why an apple seed produce apple tree? Why not the rice plant? It is very simple and interesting. We know all the offspring are similar with their parents in many respects. This property of an individual to resemble with parents is called heredity. In other words heredity is the passing of traits to offspring (from its parent or ancestors). This is the process by which an offspring acquires or becomes predisposed to the characteristics of its parent. It may be defined as transmission of characters from parents to offspring.

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Although offspring resemble with their parents in many respects, there are not exactly similar in sexual reproduction. For example, the human mother produces human child but it never resembles to either of the parents in all respects. The difference between parents and offspring or among the offspring of the same parents is called variation.

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The characteristics are determined by the DNA present in any organism. The change in heredity brings variation. Organisms interact with environment. This interaction determines what an organism is like at a given moment and what it can develop in the future.

Types of Variation:

1. Variation based on the nature of cells it affects:

On the basis of nature of cells it affects, variations are divided into two types.

a) Somatic Variation: It occurs in vegetative cell of the organism. Such variations are acquired by organism during its own life time and are lost with the death. Hence, it is also called acquired variations. They are not transmitted to offspring.

It is occurs due to the environmental effect and use and disuses of organ.

b) Germinal Variation: It occurs due to the change in germ cells. It is inheritable i.e. transfer the character from parents to offspring. It arises due to crossing over, mutation, radiation, recombination of genes etc.

2. Variation based on degree of difference:

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On the degree of difference variation is classified into two types.

a) Continuous Variation: It is small and indistinct variation found on organism during a long course of time. It is gradual, something that is not so clear cut. They are non-inheritable so they are not important from evolutionary point of view. For eg: change in weight, size, colour of the organism etc.

b) Discontinuous Variation: It is large and distinct characters of offspring which are different from parents. It is occurs due to the mutation which seen suddenly and is stable. It is inheritable. For eg: Hairless variety of dogs and cats, polydactyly etc.

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Early Views on Heredity (Pre-Mendalian Concept)

Mendel formulated different laws to explain heredity. Before him, there has been put forward different theory. Some of the theories are given below

1. Moist vapour theory: Pythagoras (550 – 500 BC) proposed moist vapour theory. According to the theory, moist vapour produced from different part of body during coitus induced the formation of embryo in uterus of female.

2. Fluid theory: It was given by Aristotle (384 – 322). According to the theory, highly purified blood which is produced by male coagulates in the body of female and form embryo. Female provides nutrition to the embryo.

3. Performation theory: It was proposed by Anton Van Leeuwenhoek (1632 – 1723). According to the theory hereditary characters are transmitted through egg or sperm or both. Gamete consists of entire organism in prefect miniature form (performationism) called homunculus. Development of an organism is a simple enlargement of homunculus.

4. Epigenesis theory: In the eighteenth century, Wolff replaced the performation theory with Epigenesis theory. According to which embryo develops gradually from a simple fertilized cell and becomes a fully developed baby in the later stage of pregnancy. Organism is not raised by the expansion of miniature form but arose by differentiation of homogenous embryonic tissue.

5. Pangeneesis theory: Pangenesis theory was proposed by Darwin (1809 – 1882) during explanation of inheritance of acquired characters. According to the theory, each organ of an organism produces very small, almost invisible identical copies of itself called pangenes or gemmules.

Gene: A gene is a sequence of nucleotides in a deoxyribonucleic acid (DNA) which codes for a particular character. It is a unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain an organism's cells and pass genetic traits to offspring.

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Properties of genes:

1) Each gene occupies a specific position in a specific chromosome. The position is called locus of the gene. Genes arrange in linear fashion.

2) Each gene has at least two alternative forms known as alleles or allelomorphs.

3) Few genes have more than two alleles called multiple alleles.

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4) Genes are capable of being copied/duplication. This process is known as replication.

5) Genes can undergo modification to form a new gene with different character. This process is known as mutation. The altered gene is transmitted from one generation to another

Function of genes:

1) Genes code for special proteins which determine the various characters/functions of a cell of the organism. Character of the organism is determined by genes.

2) They are responsible for the passage of characters from parents to offspring.

3) Differential expression of gene contained in an organism's cell give rise to various specialized cells with different characters and responsible for different functions.

Some Terminology

1) Cistron: It is the "functional unit" of DNA. It is a gene in real sense consisting of number of nucleotides and which is capable of synthesizing a polypeptide chain. S. Benzer introduced the term "cistron".

2) Muton: It is the smallest unit of DNA which can undergo mutation. It represents a change in a pair of nucleotides.

3) Recon: It is the smallest unit of DNA that can undergo recombination and crossing over.

4) Central Dogma: It is a unidirectional flow of genetic information which is transferred from DNA to protein through DNA and RNA.

DNA-------------> DNA---------------->RNA------------>protein

5) Reverse Central Dogma: It is a unidirectional flow of genetic information which is transferred from RNA to protein through DNA and mRNA.

RNA------------> DNA--------------->mRNA------------>protein

Griffith Experiment of Bacterial Transformation:

In 1928 Frederick Griffith, in a series of experiments with Diplococcus pneumonia commonly called Pneumococcus (bacterium responsible for pneumonia), witnessed a miraculous transformation. During the course of his experiment, a living organism (bacteria) had changed in physical form.

The pneumococcus bacterium occurs naturally in two forms with distinctively different characteristics.

The virulent (S-strain) form has a smooth polysaccharide capsule that is essential for infection.

The non-virulent (R-strain) lacks the polysaccharide capsule, giving it a rough appearance.

Mice injected with S-strain of the pneumococcus bacteria die from pneumonic infection within a few days, while mice injected with the R-strain bacteria continue to live. Injection with heat-killed S-strain bacteria also results in the mice surviving.

Griffith was surprised to find in his experiments that mice injected with a mixture of heat-killed S-strain and live but non-virulent R-strain produced lethal results. In fact, Griffith discovered living forms of the S-strain bacteria in the infected mice!

His experiment is tabulated as

Living R-strain + Mice --------------------> No effect

Living S-strain + Mice --------------------> Mice died due to Pneumonia

Heat killed S-strain + Mice ---------------> No effect

Heat killed S-strain + Living R-strain + Mice ------------> Mice died due to Pneumonia

He hypothesize that the R-strain bacteria had something which has been transformed by the heat-killed S-strain bacteria. Some "transforming principle", transferred from the heat-killed S-strain, had enabled the R-strain to synthesize a smooth polysaccharide coat and become virulent.

Oswald Avery, Colin McLeod, and Maclyn McCarty (1944) at the Rockefeller Institute, building on Griffith's work, showed that only DNA could cause the transformation. They isolated a cell-free extract from the S-strain bacteria and were able to transform living R-strain into a culture containing both S-strain and R-strain cells.

They performed experiment in following ways.

Polysaccharide of heat killed S-strain + Living R-strain + Mice------------> No infection in mice

Protein of heat killed S-strain + Living R-strain + Mice ---------------------> No infection in mice

DNA of heat killed S-strain + Living R-strain + Mice -----------------------> Infection in mice

DNA of heat killed S-strain + Living R-strain + DNAase + Mice ----------> No infection in mice

Nucleic Acid

Nucleic acids are non-protein, nitrogenous substances which is a macromolecule composed of chains of nucleotides. These molecules carry genetic information within cells. The most common nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nucleic acids are universal in living things. The nucleic acids DNA and RNA are made up of

a) Pentose sugar

b) Nitrogenous bases

c) Phosphoric acid

a) Pentose sugar: It is the type of sugar that contains 5 carbon atoms. It is of two types.

i) Ribose sugar: It is found in RNA. It is a water-soluble, pentose sugar (monosaccharide with five carbon atoms) that is an important component of nucleic acids, nucleotides, the vitamin riboflavin, and various co-enzymes. It has the chemical formula C₅H₁₀O₅.

ii) Deoxyribose sugar: The deoxyribose sugar in DNA is a pentose, a five-carbon sugar. Four carbons and oxygen make up the five-membered ring. It has the chemical formula C₅H₁₀O₄.

b) Nitrogenous bases: A nitrogenous (nitrogen-containing) base is an organic compound that owes its property as a base to the lone pair of electrons of a nitrogen atom. They are non-polar and due to their aromaticity, planar. In biological sciences, nitrogenous bases are typically classified as the derivatives of two parent compounds, pyrimidine and purine.

i) Pyrimidines: Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring.

It is of three types. They are Cytosine, Thymine and Uracil.

ii) Purine: A purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines are the most widely distributed kind of nitrogen-containing heterocyclic in nature.

It is of two types. They are Adenine and Guanine

c) Phosphoric Acid: It contain phosphate group.

Nucleoside: It is formed by the combination of purine or pyrimidine base linked to pentose sugar.

Nucleotide: It is formed by the combination of nucleoside with phosphoric acid.

DNA (Deoxyribonucleic Acid): Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms. The main role of DNA molecules is storage of information. The DNA segments that carry this genetic information are called genes.

DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel.

Within cells, DNA is organized into long structures called chromosomes, nucleolus, mitochondria and chloroplast.

Structure of DNA: Watson and Crick proposed the DNA model by using all the information that was available at that time. They used the data obtained from experiments carried out on DNA.

Based upon the previously obtaining facts, Watson and Crick proposed the famous DNA structure model. The important features of this model are:

1. The DNA molecule is a double helix with single polynucleotides (phosphates, sugar, base) running in opposite directions.

2. The double helix is right-handed.

3. The double helix has two different grooves.

4. The nitrogenous bases are stacked towards the inside of the helix.

5. Bases of the two polynucleotides interact by hydrogen bonding. An adenine residue in one of the polynucleotides is always adjacent to a thymine in the other strand; similarly guanine is always adjacent to cytosine.

6. Ten base pairs occur per turn of the helix. The double helix executes a turn every ten base pairs (abbreviated as 10 bp). The height or pitch of the helix is 34 A^o. The bases are stacked one on top of the other like a pile of plates. The space between the two base pairs is 8.4 A^o and has an angle of 36°.

7. The diameter of the helix is 20 A^o.

Types of DNA:

Based upon number of base pairs found in a turn, it is categorized under following types.

1. A- DNA: DNA that contains 11 base pairs per complete turns is called A- DNA. It is not found under normal physiological condition.

2. B- DNA: DNA that contains 10 base pairs per complete turns is called B- DNA.

3. C- DNA: DNA that contains 9 base pairs per complete turns is called C- DNA.

4. D- DNA: DNA that contains 8 base pairs per complete turns is called D- DNA.

5. Z- DNA: DNA that contains 12 base pairs per complete turns is called Z- DNA.

Function of DNA:

1. It acts as a carrier of genetic information from generation to generation.

2. It synthesizes ribonucleic acid (RNA) through the process of transcription.

3. It acts a prime molecule during protein synthesis.

4. It controls off the biological activities of cell.

5. DNA has autocatalytic function which directs the synthesis of its own copy.

DNA Replication:

DNA is the chemical basis of heredity, it should be able to synthesize its own replica. Watson and Crick hypothesized that the two strands of DNA untwist and separate from one another, starting from one end. During this process, covalent hydrogen bonds are broken. The separated single strands then act as templates for the synthesis of new strands. The new strands later polymerized to form complete polynucleotide chains. This process is called DNA replication.

Types of Replication:

It is mainly of three types. They are

1. Conservative replication: In this process, the parental strands are never completely separated. Hence after replication, first DNA strand contains only parental strands and the other DNA contains only daughter strand.

2. Semi- conservative replication: In this process, the two strands of DNA double helix are separated. Each of the separated strand acts as a template for the replication of new complementary strand. This produces two daughter molecules each having one new strand and one parental strand.

3. Dispersive replication: In this process, the original DNA strands break and synthesize their complementary part and recombines in a random fashion, so each strand may have old and new part.

Mechanism of Semi-Conservative mode of DNA replication:

The different steps are as follows:

1. Initiation of DNA replication: Replication starts at specific point of DNA known as origin or site of replication (Ori). In prokaryotic cell, there is one Ori where as in eukaryotic cell, number of Ori is more than one. There is formation of replication bubble due to multiple origin of DNA replication.

2. Unwinding of parental DNA: Double stranded DNA first start separating and uncoiling at least in a small region. The unwinding of DNA molecule takes place once in every ten nucleotide pairs in eukaryotic DNA. Helicase uses energy from ATP to break hydrogen bonds between base pairs. Each unwind parental DNA strand acts as a template DNA strand. When two strands unwind and separate incompletely they form a ‘Y’ shape where active synthesis occurs. This region is known as replication fork.

As the two strands are separated, a problem of positive supercoil is encountered. DNA topoisomerase has one strand cutting and strand resealing activities to prevent rewinding of DNA strand.

3. Initiation of DNA synthesis: It requires primer. The primer for DNA synthesis is a short piece of RNA that produce by RNA polymerase called primase.

4. Chain elongation: DNA polymerase III elongates a new DNA strand by adding activated deoxyribonucleotides one at a time to the 3’-OH end. Deoxyribonucleoside monophosphate is activated when they react with ATP to form deoxyribonucleoside triphosphates (dATP, dGTP, dTTP, dCTP).

During formation of phosphodiester bond between successive deoxynucleotides, two phosphate groups of deoxyribonucleotides are removed. Energy is liberated when phosphate bond is broken down, thus liberated energy is utilized for the formation of phosphodiester template. The continuous stretch of DNA in 5’-->3’ direction is called leading strand. On 5’-->3’ template there is discontinuous formation of DNA and produces short stretches of DNA which are called Okazaki fragments and the strand (3’-->5’) is called lagging strand.

5. Excision of RNA primer and their replacement by DNA: RNA primer is excised by exonuclease activity of DNA polymerase I and the gap is filled by DNA polymerase I.

6. Proof reading and DNA repair: In some cases, there is misinsertion of wrong base. The probability of misinsetion of wrong base is one in ten thousand. Correction is made during proof reading by repair enzymes.

RNA (Ribonucleic Acid): Ribonucleic acid (RNA) is a nucleic acid that contains a polymer of ribonucleotides of adenine, uracil which are joined together by phophodiester bond. It is found in nucleolus, ribosomes, mitochondria, chloroplast and cytoplasm.

Structure of RNA:

1. Primary structure of RNA: It is defined as the number of sequence of ribonucleotides in a chain. Ribonucleotides consist of ribose sugar, nitrogenous bases and phosphoric acid. It exists as single strand which are made up of ribonucleotide, bond to each other by phosphodiester bonds.

2. Secondary structure of RNA: It involves various coil formation of the polyribonucleotide chain. These coil structures are stabilized by hydrophobic interactions between purine and pyrimidine.

3. Tertiory structure of RNA: It involves the folding of the molecule into three dimensional structure.

Types of RNA:

On the basis of molecular size and functions, there are three major types of RNA

1. Ribosomal RNA (r-RNA): It is the most abundant and stable type of RNA comprising 70-80% of total cellular RNA. r-RNA is present in the ribosome. r-RNA is synthesized from the DNA of nucleolus.

2. Messenger RNA (m-RNA): It is the most heterogenous in size and stability. It carries the genetic information specifying the amino acids sequence in a protein to ribosome. m-RNA is the only type of RNA that is translated into protein. It comprises 5-10% of total RNA.

3. Transfer RNA (t-RNA): It is second most stable type of RNA. It comprises 10-15% of total RNA and it is the smallest of 3 major species of RNA. Each t-RNA serves as an “adaptor” molecule that carries its specific amino acids to the site of protein synthesis.

Heterogeneous nuclear RNA (Hn RNA or Pre-m RNA): It represents precursor of mRNA which is found only in the nucleus of eukaryotic cell.

Smaller nuclear RNA (Sn RNA): It is found in nucleus of eukaryotic cells. It participates in splicing m-RNA.

Function of RNA:

1. It plays a major role in protein biosynthesis. RNA is a working copy of DNA which helps in production of sequence of amino acids.

2. In some viruses, it acts as a hereditary material. Virus such as HIV, TMV etc. have RNA as genetic material.

Genetic Code:

The genetic code is the set of rules by which information encoded in genetic material (DNA or mRNA sequences) is translated into proteins (amino acid sequences) by living cells. The code defines from codons and amino acids. A triplet codon in a nucleic acid sequence specifies a single amino acid. Because the vast majority of genes are encoded with exactly the same code, this particular code is often referred to as the canonical or standard genetic code, or simply the genetic code, though in fact there are many variant codes.

Properties of Genetic Code:

1. Code is triplet.

2. Code is non-overlapping

3. Code is commaless

4. Code is universal

5. Code is degenerate

6. Unambiguity of code

7. Initiation codon

8. Nonsense codon

9. Colinearity

Gene Pool and Gene Frequency:

A gene pool is the collection of all the genes that exist for a given species. The bigger the gene pool, the more diverse the genetic information, and diversity as such helps populations withstand shifting, difficult environmental conditions.

For a given gene, this pool involves all the alleles of that particular gene which are present in a population. All genes or alleles are not found in equal proportion in a population.

Viral gene expression:

The meaning of virus is poisonous fluid. It is nucleoprotein which is made up of nucleic acid covered by protein coats. It was first reported by Adolf Mayer (1886) in mosaic disease in tobacco.

The term virus is first used by Beijernick (1898).

W. M. Stanley (1935) isolated a virus in crystalline form and reported that viruses were made upon exclusively of proteins.

N.W. Pirie and F.W. Bawden (1936) established that viruses were nucleoproteins.

Characteristics of viruses:

1. Viruses are the smallest and simplest of all known organisms. They can only seen with an electron microscope.

2. Viruses range in diameter from about 20 to 200 nm.

3. They are all obligate intracellular parasites and are incapable to carry out any of the typical life functions until they are inside a host cell.

4. They are parasitic on living cells but are not themselves cells.

5. They cannot be cultured on any synthetic medium.

6. They are highly specific for particular organisms.

7. Viruses exist as cubical, helical or tadpole shaped structures.

8. Viruses lack the enzymes necessary for the generation of energy.

9. They are capable of self reproduction inside the host cell.

10. They can be crystallized from suspensions.

Gene expression in Virus:

Virus consists of very few genes. The expression of viral gene takes place only inside the host.

The virus is going to follow a lytic or a lysogenic cycle. In a lytic cycle, it undergoes replication and produces more phages while in a lysogenic cycle, it may remain as temperate, it gives rise to a prophage as its DNA integrates with the bacterial DNA.

1. Lytic Cycle: The lytic cycle is typically considered the main method of viral replication, since it results in the destruction of the infected cell.

Viruses of the lytic cycle are called virulent viruses. The lytic cycle is a six-stage cycle. In the first stage, the virus injects its own nucleic acids into a host cell. Then the viral acids form a circle in the center of the cell. The cell then mistakenly copies the viral acids instead of its own nucleic acids. Then the viral DNA organizes themselves as viruses inside the cell.

The reproductive process of virulent phage is called lytic cycle because the host is lysed at the end and virus particles release. Lytic cycle is common in T₂, T₄ bacteriophage. The process is divided into following stages.

a) Adsorption: The bacteriophage gets attached to the wall of bacterium by its tail fibres. It brings tip of the tail in contact with host cell wall.

b) Penetration: This stage is the injection of nucleic acid of the virus into the host cell. The tail sheath contracts and the enzyme lysozyme helps in creating a hole in the cell wall so, as to inject phage DNA into the bacterial cell. The protein coat remains outside, attached to the cell wall.

c) Eclipse stage: The phage DNA now codes for the phage enzymes using the host machinery. The enzyme nuclease produced by the expression of viral gene breaks down the host DNA. Enzyme nuclease fails to harm phage DNA as it contains modified cytosine residues. Cytosine residues make phage DNA resistant to nuclease attack. The phage DNA replicates and codes for new coat proteins.

d) Maturation stage: In this stage, the new phage particles are made by the assembly of protein coats surrounding the phage DNA.

e) Lysis of host and release of virus particles: The lysozyme made by phage DNA brings about the lysis of the bacterial cell releasing the phages, ready to infect more bacteria. Such a cycle, where phage bring about the disintegration or lysis of the bacterium, is called as lytic cycle.

2. Lysogenic Cycle: Lysogeny, or the lysogenic cycle, is methods of viral reproduction (the lytic cycle is the other). Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome. Lysogenic cycles can also occur in eukaryotes, although the method of incorporation of DNA is not fully understood. Certain types of viruses replicate by the lysogenic cycle, but also partly by the lytic cycle (mixed cycles).

The adsorption and the penetration phases are same as in lytic cycle. In the process, DNA integrates with the bacterial DNA and does not exert any influence over the bacterial cell. DNA which is intregrated with bacterial DNA is called prophage or provirus.

The phage DNA also replicates along with the host DNA. A repressor protein produced by the prophage keeps the phage genes in repressed stage. In this way, phage DNA may keep multiplying the prophage generation after generation without causing any damage to host. Such a bacterial cell that carries the potential seed of destruction by carrying prophage is called as lysogenic cell. The phenomenon by which phage DNA becomes a part of host cell is called as lysogeny.

Reverse Transcription: A reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase enzyme that transcribes single-stranded RNA into double-stranded DNA. It also helps in the formation of a double helix DNA once the RNA has been reverse transcribed into a single strand DNA. Normal transcription involves the synthesis of RNA from DNA.

Well studied reverse transcriptases include:

# HIV-1 reverse transcriptase from human immunodeficiency virus type 1 (PDB 1HMV)

# M-MLV reverse transcriptase from the Moloney murine leukemia virus

# AMV reverse transcriptase from the avian myeloblastosis virus

# Telomerase reverse transcriptase that maintains the telomeres of eukaryotic chromosomes

Process of reverse transcription

Reverse transcriptase creates single stranded DNA from an RNA template.

In virus species with reverse transcriptase lacking DNA-dependent DNA polymerase activity, creation of double-stranded DNA can possibly be done by host-encoded DNA polymerase δ, mistaking the viral DNA-RNA for a primer and synthesizing a double-stranded DNA by similar mechanism as in primer removal, where the newly synthesized DNA displaces the original RNA template.

Gene Expression in Prokaryotes:

Bacteria consist of DNA as genetic material and it is found in two separate genomes. The first type is the double stranded circular DNA which is relatively larger in size. It is called nucleoid or chromosomal DNA. In addition to nucleoid, bacterial cytoplasm normally contains many small, separate, circular, self replicating, extra chromosomal DNA which are called plasmids. Plasmids which can temporarily integrate into nucleoid and replicate with it are called episomes. Plasmid carry gene as fertility factor (F⁺ plasmid), colicinogen factor (Col plasmid), R factor (R plasmid) etc. Genes of nucleoid express for the synthesis of chemicals for the living and survival of bacteria.

Genetic Recombination in Bacteria:

Bacteria have no sexual reproduction in the sense that eukaryotes do. The have

· no alternation of diploid and haploid generations

· no gametes

· no meiosis

But the essence of sex is genetic recombination, and bacteria do have three mechanisms to accomplish. They are:

· transformation

· conjugation

· transduction

Transformation: Transformation is the genetic alteration of a cell resulting from the uptake, incorporation and expression of exogenous genetic material (DNA) that is taken up through the cell wall(s). Transformation occurs most commonly in bacteria and in some species. Transformation can also be effected by artificial means. Bacteria that are capable of being transformed, whether naturally or artificially, are called competent.

Transformation was first demonstrated in 1928 by Frederick Griffith, an English bacteriologist searching for a vaccine against bacterial pneumonia. Griffith discovered that a harmless strain of Streptococcus pneumoniae. DNA of donor bacterium is incorporated into the DNA of recipient bacterium forming recombinant DNA. Genes present in donor DNA express and change the characteristics of recipient.

Stages in Transformation:

Transformation goes through three stages:

1. In the first stage, cell becomes competent. Competence is the ability of cells to take up DNA through changes in the cell wall. This involves the formation or activation of special DNA receptor protein.

2. The second stage is DNA binding and uptake. This involves interaction between the cell wall receptors and the donor DNA.

3. The third step involves intracellular transport of transforming DNA to recipient. A single strand of donor DNA is incorporated into the recipient DNA by displacing a homologous section of one of the recipient DNA strand. The integrated donor strand then replicates forming double helix.

Transduction: Transduction is the process by which DNA is transferred from one bacterium to another by a virus. It also refers to the process whereby foreign DNA is introduced into another cell via a viral vector.

When bacteriophages (viruses that infect bacteria) infect a bacterial cell, their normal mode of reproduction is to harness the replicational, transcriptional, and translation machinery of the host bacterial cell to make numerous virions, or complete viral particles, including the viral DNA or RNA and the protein coat.

Methods of Transduction

The packaging of bacteriophage DNA has low fidelity and small pieces of bacterial DNA, together with the bacteriophage genome, may become packaged into the bacteriophage genome. At the same time, some phage genes are left behind in the bacterial chromosome.

Generalized transduction

Generalized transduction may occur in two main ways, recombination and headful packaging.

If bacteriophages undertake the lytic cycle of infection upon entering a bacterium, the virus will take control of the cell’s machinery for use in replicating its own viral DNA. If by chance bacterial chromosomal DNA is inserted into the viral capsid used to encapsulate the viral DNA, the mistake will lead to generalized transduction.

The new virus capsule now loaded with part bacterial DNA continues to infect another bacterial cell. This bacterial material may become recombined into another bacterium upon infection.

When the new DNA is inserted into this recipient cell it can fall to one of three fates

a) The DNA will be absorbed by the cell and be recycled for spare parts.

b) If the DNA was originally a plasmid, it will re-circularize inside the new cell and become a plasmid again.

c) If the new DNA matches with a homologous region of the recipient cell’s chromosome, it will exchange DNA material similar to the actions in conjugation.

This type of recombination is random and the amount recombined depends on the size of the virus being used.

Specialized transduction

The second type of recombination event is called specialized transduction and occurs as a result of mistakes in the transition from a virus' lysogenic to lytic cycle. If a virus incorrectly removes itself from the bacterial chromosome, bacterial DNA from either end of the phage DNA may be packaged into the viral capsid. Specialized transduction leads to three possible outcomes:

a) DNA can be absorbed and recycled for spare parts.

b) The bacterial DNA can match up with a homologous DNA in the recipient cell and exchange it. The recipient cell now has DNA from both itself and the other bacterial cell.

c) DNA can insert itself into the genome of the recipient cell as if still acting like a virus resulting in a double copy of the bacterial genes.

Example of specialized transduction is λ phages in Escherichia coli.

Conjugation: Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells. It is discovered in 1946 by Joshua Lederberg and Edward Tatum.

Bacterial conjugation is often incorrectly regarded as the bacterial equivalent of sexual reproduction or mating since it involves the exchange of genetic material. During conjugation the donor cell provides a conjugative is most often a plasmid. Most conjugative plasmids have systems ensuring that the recipient cell does not already contain a similar element.

The genetic information transferred is often beneficial to the recipient. Benefits may include antibiotic resistance, xenobiotic tolerance or the ability to use new metabolites. Such beneficial plasmids may be considered bacterial endosymbionts.

Differences between Transformation and Transduction

Transformation	Transduction
1. It is the transfer of DNA from donor to recipient. It does not require virus. 2. Many genes may be transferred. 3. It involves absorption of genes. 4. Calcium chloride is necessary.	1. It is the transfer of DNA from donor to recipient bacterium by virus. 2. Only 1-2 genes are transferred. 3. Transduction involves carrying genes from a living host. 4. It does not require calcium chloride.

Gene expression in Eukaryotes:

Genetic expression and regulation in eukaryotes is very much complicated than that of the prokaryotes. The DNA of eukaryotes is packed in chromosome where it is associated with different molecules including histone proteins.

DNA molecules are surrounded by octamer of histone complex which is formed by four kinds of histone proteins namely H_1A, H_2B, H₃ and H₄. Each histone protein has two molecules in octamer of histone to form beaded structures called nucleosomes. Several nucleosomes are gathered in certain areas called chromomeres. Uncoiling of DNA is necessary for transcription. In addition to histone proteins, RNA and non-histone proteins are also associated with DNA and they may also take part in regulation of gene expression in higher organisms.

All genes present in chromosome are not functional. Some genes of certain areas are not functional. Such areas are called heterochromatin whereas other part contains functional genes where DNA is relatively uncoiled. Such area is called euchromatin. So, higher the uncoiling of DNA, higher will be the gene expression.

Some Important Terms:

Capsid: It is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic material of the virus.

Co-repressor: A protein that decreases gene expression by binding to a transcription factor which contains a DNA binding domain. The co-repressor is unable to bind DNA by itself. This increases the positive charge on histones which strengthens in the interaction between the histones and DNA, making the latter less accessible to transcription.

Exon: A nucleic acid sequence that is represented in the mature form of an RNA molecule after either portions of a precursor RNA (introns) have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA or a functional form of a non-coding RNA such as rRNA or tRNA. Depending on the context, exon can refer to the sequence in the DNA or its RNA transcript.

Intron: A DNA region within a gene that is not translated into protein. These non-coding sections are transcribed to precursor mRNA (pre-mRNA) and some other RNAs (such as long noncoding RNAs), and subsequently removed by a process called splicing during the processing to mature RNA. After intron splicing (ie. removal), the mRNA consists only of exon derived sequences, which are translated into a protein.

The word intron is derived from the term intragenic region and also called intervening sequence (IVS)

Inducer: The DNA sequence must be copied to make a smaller, mobile molecule called messenger RNA (mRNA), which carries the instructions for making a protein to the site where the protein is manufactured. Many different types of proteins can affect the level of gene expression by promoting or preventing transcription. In prokaryotes (such as bacteria), these proteins often act on a portion of DNA known as the operator at the beginning of the gene. The operator is where RNA polymerase, the enzyme which copies the genetic sequence and synthesizes the mRNA, attaches to the DNA strand.

Inducers function by disabling repressor proteins. Repressor proteins bind to the DNA strand and prevent RNA polymerase from being able to attach to the DNA and synthesize mRNA. Inducers bind to repressors, causing them to change shape and preventing them from binding to DNA. Therefore, they allow transcription, and thus gene expression, to take place. Some inducers are modulated by activators, which have the opposite effect on gene expression as repressors. Inducers bind to activator proteins, allowing them to bind to the DNA strand where they promote RNA transcription.

Oncogene: An oncogene is a gene that is mutated or expressed at high levels, and thus helps turn a normal cell into a tumor cell.

Many abnormal cells normally undergo a programmed form of death (apoptosis). Activated oncogenes can cause those cells to survive and proliferate instead. Most oncogenes require an additional step, such as mutations in another gene, or environmental factors, such as viral infection, to cause cancer. Since the 1970s, dozens of oncogenes have been identified in human cancer. Many cancer drugs target those DNA sequences and their products.

Operon: An operon is a functioning unit of genomic material containing a cluster of genes under the control of a single regulatory signal or promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create monocistronic mRNAs that are translated separately, i.e. several strands of mRNA that each encode a single gene product. The result of this is that the genes contained in the operon are either expressed together or not at all. Originally operons were thought to exist solely in prokaryotes but since the discovery of the first operons in eukaryotes in the early 1990s, more evidence has arisen to suggest they are more common than previously assumed. Several genes must be both co-transcribed and co-regulated to define an operon.

Lysogeny: Lysogeny, or the lysogenic cycle, is one of two methods of viral reproduction (the lytic cycle is the other). Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome.

XAVIER INTERNATIONAL COLLEGE

2010-12-01T05:40:00.000-08:00

Ghale Gaun Village Tour Program Programs:2Night / 3 Days

1st day

· Drive for Beshishar at 9 PM

· Breakfast in Beshishar at 6:30 AM

· 7:30 AM Walk Start for Ghale gaun

· Lunch on the way 12 PM

· More 2:30 hour walk for Ghale Gaun

· Welcome by Ghale Gaun Villagers 4 PM

· Dinner ( Typical Nepali Food )

· Cultural Programes

· Overnight at Ghale gaun Village

2nd day

· Wake up followed By organic Tea 6 AM

· Sight seeing of Himalayas ( Annapurna , Manaslu , Lamjung , Fishtail, and many more vistas )

· Heavy Breakfast 7 AM

· Village Tour of Ghan Pokhara ( A near village located in near by hill belongs to honey hunters )

· Lunch 12 PM

· Detail Village tour of Ghale gaun ( Explore Yourself)

· Interaction with Villagers

· Great Himalayan Gurung Museum visit

· Evening Lunch 7 PM

· Cultural Performance

· Overnight at Ghale Gaun

3rd Day

· Wake up at 6 AM

· Early Morning Breakfast

· Departure for Khudi ( 4 hour adventure Jungle walk)

· Lunch at Beshishar 12 Pm

· Drive for Kathmandu

Total cost for the trip-:3200NRS

Ghale Gaun

2010-12-01T05:28:00.000-08:00

Ghalegaun situated at the foot of Lamjung Himal in north central Nepal, is an exotic pristine village endowed with an unparallel scenic grandeur and a home to world famous Gurkha soldiers- the Gurungs. Repository of a unique ethnic culture Ghalegaun is a true microcosm of stunning natural beauty mixed with an unspoiled ethnic lifestyle. Ghanapokhara is a beautiful village heading towards development with a concept of eco-tourism. It lies at north of Lamjung district in the close proximity of Ghalegaun at the top of Dashthar Danda at an altitude of 2100 meters.

FAST FACTS . Location: 205 km northwest of Kathmandu

. Elevation: 2,016 m

. Highlights: Ghale (Gurung) lifestyle, Himalayan views

. Getting there: Four-hour walk from Khudi, which is connected by daily bus services from Kathmandu and Pokhara

. Accommodation: Home stay in Ghale Gaun lodges in Khudi

Ghalegaun and Ghanpokhara are mainly Gurung settlements; they nestle amidst mountains, rivers, streams, waterfalls and green forests. These places command a superb breathtaking view of majestic western Himalayas including Machhapuchhare(6693m) Annapurna (8091m), Annapurna II (7939m) Annapurna IV (7525m), Lamjung Himal, Bouddha Himal(6974m), Himalchuli (6747m) and many more smaller peaks.

The approach to Ghalegaun-Ghanpokhara is a wonderful experience in itself as it goes crossing over the Marsyandi, Khudi and Midim rivers; passing through rhododendrons blossoming along the way amidst the chirping of birds and wild insects. The trekking route passes through dense jungle and villages and impressive waterfalls. Nearby Talyngo Lake and Lami Lake add new dimension to these attractions.

Activities around this village including bird watching at Talangyo lake, and visitors to the Utter Kanya temple, Pempro fall, Batase cave and the Khudi hydroelectric dam site.

Cultural Attractions

Ghalegaun -Ghanpokhara are model villages for experiencing the typical culture and lifestyle of the Gurung people. Traditional customs are still followed during births, deaths, marriages and at other important times in a person`s life. Age-old cultural dances like the Jhyaure, Serka, Dohori, Ghantu, Ghyabring, Krishna Charitra and Jhakri are performed on various occasions accompanied by different musical instruments with the dancers in traditional dress.

Visitors to Ghalegaun-Ghanpokhara are welcomed with offering of garlands and tika while music and dances are performed and traditional farewell songs are sung when guests depart. Nepali New Year and Buddha Jayanti are celebrated with traditional dance called Ghatu.

Handicrafts

The people of Ghalegaun-Ghanpokhara keep goats and sheep and use wool from these animals to make woolen products. They make clothes and bags from nettle fiber (allo cloth) and scarfs, towels and shawls from the wool of angora rabbits. Ironsmiths make different iron products. Craftsmen produce a whole range of different products from bamboo.

Getting There

Ghalegaun and Ghanpkhara lie 205 kilometers northwest of Kathmandu and 125 kilometers northeast of Pokhara. The nearest roadhead is at Khudi in Lamjung; Khudi can be reached by daily bus services from Kathmandu and Pokhara. The hotels in Khudi provide safe stay with hygienic food; pleasant rooms, clean restrooms and some even have natural swimming pools nearby. Ghalegaun is a four-hour walk from Khudi through another Gurung settlement Bhalam Chour. The way from Bhalam Chour to Ghalegaun through the thick forest provides opportunities to see many species of animals, birds, insects and butterflies. Ghanpokhara is also a three- hour walk from Khudi but it can be also be reached from Beshisahar crossing Kapur Gaon without reaching Khudi.

Organized tourist groups are welcomed into Ghalegaun and Ghanpokhara with traditional dances. Handicraft exhibition and other entertainment programs are also performed for visitors. Tourists can participate in traditional musical program of Rodhi every evening. Trekking to and staying at Ghalegaun and Ghanpokhara is an exciting and enjoyable experience for both international and domestic visitors. Special discount facilities are offered to groups of students, forest users, women and community members.

Lodging and fooding

Comfortable rooms with clean restrooms are available at selected Gurung houses. Although there is no electricity in the village, lamps and water heating system facilities are available through solar power. There are a few Pahuna Ghar (Guest House) belonging to the Aama Samuha (Mother`s Community) that also provide accommodation. More than 100 tourists can be accomodated both in Ghalegaon and Ghanpokhara seperately. Good camping sites are also available at both Ghalegaun and Ghanpokhara. Organic local food like cereals, vegetables, milk products, eggs and meat prepared in traditional way is served to visitors. Basic menu includes plain rice, vegetable curry, vegetable fried rice, chicken curry, dal-bhat, egg curry, dhendo soup, chapatti, garlic soup, bread, vegetable mixed soup and momo.

Views of Ghale Gaun

2010-11-27T03:33:00.000-08:00

Ghale Gaun(lumjung)

2010-11-27T03:11:00.000-08:00

This Is For Student Of Xavier International College

Ghale Gaun

. Location: 205 km northwest of Kathmandu

. Elevation: 2,016 m

. Highlights: Ghale (Gurung) lifestyle, Himalayan views

. Getting there: Four-hour walk from Khudi, which is connected by daily bus services from Kathmandu and Pokhara

. Accommodation: Home stay in Ghale Gaun lodges in Khudi

Activities around this village including bird watching at Talangyo lake, and visitors to the Utter Kanya temple, Pempro fall, Batase cave and the Khudi hydroelectric dam site.

Cultural Attractions

Handicrafts

Getting There

Lodging and fooding

khagendra acharya

What Teenage Love is

2010-11-14T04:44:00.000-08:00

In life, people fall in love at many stages. It is very possible for every person no matter their age to feel or fall in love. However, there is a certain stage in life where we reach and everyone seems to want love. I'm talking about the teenage years and love. When a teenager falls in love, it is referred to as teenage love. Teens are very volatile people and this is pretty understandable. It is the first time in life to feel the urge to love the opposite sex. This is on the onset of their physical growth. Their hormones are usually referred to as running wild and this is very much the case. Teenage is a confusing place to be because you are not old enough to be called mature and you are not too young to be called a child. This is the time where most youth act out and when it comes to the matters of the heart, a lot of them fall in love. Teenage love has sometimes been referred to as not being real love. Instead, experts say that a lot of feelings that teens have for the opposite sex is mainly infatuation. This is a form of lust that passes with time.

However, love being hard to define, it is vital that all cases be looked at differently. It is during this stage that many teens make the worse mistakes of their lives but, this is usually not the case in other situations. Sexually, teens what to experience and explore first hand, the kind of emotions that are associated with love. It is therefore paramount to understand exactly what they are going through before you are quick to give them advice. The biggest issue that is always a source of debate is sex during teenage. Many want to know what it is all about. Others believe that for love to be real there must be sexual intercourse. With the modern world, more and more teens are having choices when it comes to sex. Many have not come up openly to condemn teenage sex. In the past, when young people reached teenage, this was a time for them to be married off. For this reason, teens cannot be totally condemned for wanting to exercise that which has been there since time began.
However, with civilization, more and more parents have come out strongly to condemn any love consummation for their teens.

The question whether this is real love or not, still remains as more teens get involved emotionally with other people. One thing that we can say for sure is that, if the love during teenage is not real; the person involved will have to learn through experience. Thankfully, teenage is only a phase of life and as you grow, you will discover things and become wiser in the matter of love. However, when it comes to love, no one can claim to be an expert. It comes without mention and no one has control over it. Therefore, the best thing that teens can do is to empower themselves and know how to handle themselves when it comes to matters of the heart. Otherwise, love is meant to be enjoyed to the fullest.

NASA Finds Fresh Evidence of Water on Mars

2010-11-13T18:20:00.000-08:00

NASA says it has found new evidence of water below the surface of Mars.

Scientists studying the composition of the ground near where a Mars exploration rover got stuck found evidence that water had seeped through the ground, dissolving and carrying away certain minerals. The water may have come from melted snow or ice.

There is lots of evidence that there was once liquid water on Mars, including dried-up lake beds and valleys. But these were formed more than a billion years ago.

The new study is the first sign of the presence of liquid water in more recent times.

"This is a process that's ongoing; it's not an ancient process," Ray Arvidson, deputy principal investigator for the Mars rovers, told AOL News.

The Mars Exploration Rover Spirit got stuck in April 2009, with its left wheels breaking through a crust and into soft sand below.

The presence of liquid water on Mars could be useful for any potential colonists. Pete Worden, NASA Ames Research Center director, recently introduced a project to embark on a one-way mission from Earth to Mars by 2030 and permanently settle the red planet. The project is called the Hundred Year Starship initiative.

"The human space program is now really aimed at settling other worlds," Worden said. "Twenty years ago you had to whisper that in dark bars and get fired."

Earth's neighbor is the fourth planet in the solar system from the sun and has long been thought the most likely candidate to support life. A NASA probe previously discovered a large amount of ice at the south pole of Mars.

Still, the new discovery is far from conclusive evidence that Mars could support life. The changes in the soil point toward tiny droplets of water, rather than rivers or oceans.

"Liquid water and life kind of go together," Arvidson said. But "it's got to be a very tough life" to survive in such a small amount of water.

Peer Pressure and Teen Sex

2010-11-12T06:09:00.000-08:00

Many teens, especially boys, feel pressure to have sex before they are ready. According to recent research, some 63 percent of teens believe that waiting to have sex is a good idea, but few people actually do

Many teens, especially boys, feel pressure to have sex before they are ready. According to research released this week, some 63 percent of teens believe that waiting to have sex is a good idea, but few people actually do.

One in three boys ages 15-17 say they feel pressure to have sex, often from male friends. Teen girls feel less pressure--only 23 percent said they felt such coercion. Researchers questioned 1,854 subjects between the ages of 13 and 24 in a national survey.

The study, released by the Kaiser Family Foundation, also found that teens feel strong pressure to drink and try drugs. The study findings show a need for sex education at a young age, say the study authors.

A separate study released this week, sponsored by the National Campaign to Prevent Teen Pregnancy, finds that one in five teens reported having sex before they were 15. One in seven sexually active 14-year-olds also said they have been pregnant.

Still, other research is not as pessimistic about teen sexuality. Studies have found that teens were less sexually active during the 1990s compared with decades before. The overall rate of sexual activity declined by 5.7 percent, and the number of pregnancies, abortions and sexually transmitted diseases also fell in the last decade.

An Inconvenient Truth: Global Warming

2010-11-11T05:42:00.000-08:00

An Inconvenient Truth: Global Warming

Global Warming or Climate Change, measurable increases in the average temperature of Earth’s atmosphere, oceans, and landmasses. Scientists believe Earth is currently facing a period of rapid warming brought on by rising levels of heat-trapping gases, known as greenhouse gases, in the atmosphere.
Greenhouse gases retain the radiant energy (heat) provided to Earth by the Sun in a process known as the greenhouse effect. Greenhouse gases occur naturally, and without them the planet would be too cold to sustain life as we know it. Since the beginning of the Industrial Revolution in the mid-1700s, however, human activities have added more and more of these gases into the atmosphere. For example, levels of carbon dioxide, a powerful greenhouse gas, have risen by 35 percent since 1750, largely from the burning of fossil fuels such as coal, oil, and natural gas. With more greenhouse gases in the mix, the atmosphere acts like a thickening blanket and traps more heat.

Earth has warmed and cooled many times since its formation about 4.6 billion years ago. Global climate changes were due to many factors, including massive volcanic eruptions, which increased carbon dioxide in the atmosphere; changes in the intensity of energy emitted by the Sun; and variations in Earth’s position relative to the Sun, both in its orbit and in the inclination of its spin axis.
Variations in Earth’s position, known as Milankovitch cycles, combine to produce cyclical changes in the global climate. These cycles are believed to be responsible for the repeated advance and retreat of glaciers and ice sheets during the Pleistocene Epoch (1.8 million to 11,500 years before present), when Earth went through fairly regular cycles of colder “glacial” periods (also known as ice ages) and warmer “interglacial” periods. Glacial periods occurred at roughly 100,000-year intervals.

An interglacial period began about 10,000 years ago, when the last ice age came to an end. Prior to that ice age, an interglacial period occurred about 125,000 years ago. During interglacial periods, greenhouse gases such as carbon dioxide and methane naturally increase in the atmosphere from increased plant and animal life. But since 1750 greenhouse gases have increased dramatically to levels not seen in hundreds of thousands of years, due to the rapid growth of the human population combined with developments in technology and agriculture. Human activities now are a powerful factor influencing Earth’s dynamic climate.

The ice of the polar regions furnishes clues to the makeup of Earth’s ancient atmosphere. Ice cores that scientists have bored from the ice sheets of Greenland and Antarctica provide natural records of both temperature and atmospheric greenhouse gases going back hundreds of thousands of years. Layers in these ice cores created by seasonal snowfall patterns allow scientists to determine the age of the ice in each core. By measuring tiny air bubbles trapped in the ice and properties of the ice itself, scientists can estimate the temperature and amount of greenhouse gases in Earth’s past atmosphere at the time each layer formed. Based on this data, scientists know that greenhouse gases have now risen to levels higher than at any time in the last 650,000 years.

Greenhouse gases are rising, and temperatures are following. Before the late 1800s, the average surface temperature of Earth was almost 15°C (59°F). Over the past 100 years, the average surface temperature has risen by about 0.7 Celsius degrees (1.3 Fahrenheit degrees), with most of the increase occurring since the 1970s. Scientists have linked even this amount of warming to numerous changes taking place around the world, including melting mountain glaciers and polar ice, rising sea level, more intense and longer droughts, more intense storms, more frequent heat waves, and changes in the life cycles of many plants and animals. Warming has been most dramatic in the Arctic, where temperatures have risen almost twice as much as the global average.

Scientists project global warming to continue at a rate that is unprecedented in hundreds of thousands or even millions of years of Earth’s history. They predict considerably more warming in the 21st century, depending on the level of future greenhouse gas emissions. For a scenario (possible situation) assuming higher emissions—in which emissions continue to increase significantly during the century—scientists project further warming of 2.4 to 6.4 Celsius degrees (4.3 to 11.5 Fahrenheit degrees) by the year 2100. For a scenario assuming lower emissions—in which emissions grow slowly, peak around the year 2050, and then fall—scientists project further warming of 1.1 to 2.9 Celsius degrees (1.9 to 5.2 Fahrenheit degrees) by the year 2100.
Melting polar ice and glaciers, as well as warming of the oceans, expands ocean volume and raises sea level, which will eventually flood some coastal regions and even entire islands. Patterns of rainfall are expected to change, with higher latitudes (closer to the poles) projected to receive more rainfall, and subtropical areas (such as the Mediterranean and southern Africa) projected to receive considerably less. Changes in temperature and precipitation patterns may damage food crops, disrupting food production in some parts of the world. Plant and animal species will shift their ranges toward the poles or to higher elevations seeking cooler temperatures, and species that cannot do so may become extinct. Increasing levels of carbon dioxide in the atmosphere also leads to increased ocean acidity, damaging ocean ecosystems.

Human beings face global warming with a huge population at risk. The potential consequences are so great that many of the world’s leading scientists—and increasingly, politicians, business leaders, and other citizens—are calling for international cooperation and immediate action to counteract the problem.

Technology

2010-11-11T05:34:00.000-08:00

In the field of communications, Italian electrical engineer Guglielmo Marconi sent his first radio signal across the Atlantic Ocean in 1901. American inventor Lee De Forest invented the triode, or vacuum tube, in 1906. The triode eventually became a key component in nearly all early radio, radar, television, and computer systems. In 1920 Scottish engineer John Logie Baird developed the Baird Televisor, a primitive television that provided the first transmission of a recognizable moving image. In the 1920s and 1930s American electronic engineer Vladimir Kosma Zworykin significantly improved the television’s picture and reception. In 1935 British physicist Sir Robert Watson-Watt used reflected radio waves to locate aircraft in flight. Radar signals have since been reflected from the Moon, planets, and stars to learn their distance from Earth and to track their movements (see Radar Astronomy).
In 1947 American physicists John Bardeen, Walter Brattain, and William Shockley invented the transistor, an electronic device used to control or amplify an electrical current. Transistors are much smaller, far less expensive, require less power to operate, and are considerably more reliable than triodes. Since their first commercial use in hearing aids in 1952, transistors have replaced triodes in virtually all applications.

During the 1950s and early 1960s minicomputers were developed using transistors rather than triodes. Earlier computers, such as the electronic numerical integrator and computer (ENIAC), first introduced in 1946 by American physicist John W. Mauchly and American electrical engineer John Presper Eckert, Jr., used as many as 18,000 triodes and filled a large room. But the transistor initiated a trend toward microminiaturization, in which individual electronic circuits can be reduced to microscopic size. This drastically reduced the computer’s size, cost, and power requirements and eventually enabled the development of electronic circuits with processing speeds measured in billionths of a second .

Further miniaturization led in 1971 to the first microprocessor—a computer on a chip. When combined with other specialized chips, the microprocessor becomes the central arithmetic and logic unit of a computer smaller in size than a portable typewriter. With their small size and a price less than that of a used car, today’s personal computers are many times more powerful than the physically huge, multimillion-dollar computers of the 1950s. Once used only by large businesses, computers are now used by professionals, small retailers, and students to perform a wide variety of everyday tasks, such as keeping data on clients, tracking budgets, and writing school reports. People also use computers to interface with worldwide communications networks, such as the Internet and the World Wide Web, to send and receive e-mail, to shop, or to find information on just about any subject.

During the early 1950s public interest in space exploration developed. The focal event that opened the space age was the International Geophysical Year from July 1957 to December 1958, during which hundreds of scientists around the world coordinated their efforts to measure the Earth’s near-space environment. As part of this study, both the United States and the Soviet Union announced that they would launch artificial satellites into orbit for nonmilitary space activities.

When the Soviet Union launched the first Sputnik satellite in 1957, the feat spurred the United States to intensify its own space exploration efforts. In 1958 the National Aeronautics and Space Administration (NASA) was founded for the purpose of developing human spaceflight. Throughout the 1960s NASA experienced its greatest growth. Among its achievements, NASA designed, manufactured, tested, and eventually used the Saturn rocket and the Apollo spacecraft for the first manned landing on the Moon in 1969 (see Apollo Program). In the 1960s and 1970s, NASA also developed the first robotic space probes to explore the planets Mercury, Venus, and Mars (see Mariner). The success of the Mariner probes paved the way for the unmanned exploration of the outer planets in Earth’s solar system.
In the 1970s through 1990s, NASA focused its space exploration efforts on a reusable space shuttle, which was first deployed in 1981. In 1998 the space shuttle, along with its Russian counterpart known as Soyuz, became the workhorses that enabled the construction of the International Space Station.

Energy from Heat

2010-11-02T19:33:00.000-07:00

Energy means power—the power to do work. And thermal, or heat, energy can do a lot of work. When heat is applied to water, for instance, it makes the water boil. Boiling water then changes to vapor, or steam, which can apply great force as it escapes a container. Large quantities of steam powered the earliest train engines.
The most important source of thermal energy for our Earth is the Sun’s rays. This “solar energy” is used to heat houses, water, and, in some countries, ovens used for cooking. Solar power can even be converted to electricity and stored for later use.
To human beings the second most important source of thermal energy is the store of natural fuels on and in the Earth. When these fuels—mainly coal, oil, gas, and wood—are burned, they produce heat. This heat can be used for warmth, made to power a machine directly, or converted into electricity. For example, a car engine burns gasoline (an oil product) for direct thermal power. In some areas coal is burned to produce the electricity that powers people’s homes.
In a very few parts of the world, an interesting third form of heat energy comes from “living” heat inside the Earth itself. This “geothermal energy” comes from such sources as natural hot springs and the heat of active volcanoes (“geo-” means “earth”). Naturally escaping steam and hot water are used to heat and power homes and businesses in Reykjavik, Iceland. And though volcanoes are mostly too hot to tap directly, worldwide experiments continue as other major fuel supplies dwindle.

The Greenhouse Effect

2010-11-02T19:25:00.000-07:00

THE ‘‘GREENHOUSE EFFECT’’ REFERS TO THE PROCESS by which infrared radiation-absorbing gases in Earth’s atmosphere trap heat and thus influence climate. This article gives an overview of the anthropogenic loading of greenhouse gases into the atmosphere and associated effects on recent and future climate change, summarizes feedback effects, and describes potential and current impacts of climate change on biodiversity.
Earth’s climate, from daily weather events to glacial and interglacial cycles, is driven by the amount of radiation received from the sun and how that radiation is distributed throughout the global Earth–atmosphere system. The atmospheric greenhouse effect acts as an important factor in establishing a temperature that is hospitable for life. The basic mechanism is simple and was first detailed by the Swedish physicist Svante August Arrhenius in 1896. Light from the sun largely penetrates the atmosphere and is absorbed at the planetary surface. There, it is converted from energy in the form of light to energy in the form of heat (longwave infrared radiation). As the surface temperature rises because of this heat, Earth radiates more and more heat back out to space, thereby maintaining an energy balance. Several gases in the atmosphere, referred to as ‘‘greenhouse gases,’’ absorb some of the heat emitted from Earth’s surface and reradiate it back toward the surface, causing the temperature to rise. Without this naturally occurring greenhouse effect, Earth’s average surface temperature would be _19_C, about 33_C colder than it is today. The term ‘‘greenhouse effect,’’ though popular, is a misnomer because the warming effect of glass greenhouses is due primarily to suppression of convection, not trapping of infrared radiation.
The most important naturally occurring greenhouse gases are water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). Although water vapor plays the biggest role in generating the natural greenhouse effect, anthropogenic emission of the other gases, along with artificially produced chlorofluorocarbons (CFCs), are most important in generating an enhanced greenhouse effect. Detailed instrument data show that concentrations of these gases have been increasing since preindustrial times (_1750) (Table I), particularly in recent decades, largely due to human industrial, agricultural, and urbanization activities. As the concentrations of greenhouse gases increase in the atmosphere, they continue to trap and reradiate more and more heat, resulting in rising surface temperature and other climatic changes. Increases in CO2 account for about 65% of the current direct positive radiative forcing due to anthropogenic loading of greenhouse gases (Fig. 1). The atmospheric CO2 concentration has increased 30% since preindustrial times, as a result of increasing emissions from fossil fuel combustion, land conversion, and cement production, and is continuing to increase by 0.4% per year (Fig. 2). If future emissions of CO2 are maintained at 1994 levels, its atmospheric concentration will be close to double the preindustrial level by the end of the twenty-first century. In the absence of strong emissions controls, given increasing global energy and resource consumption, CO2 concentrations may double by 2040 and will continue to increase dramatically Concentrations of other greenhouse gases, particularly methane and nitrous oxide, are also expected to rise, resulting in an earlier doubling of the equivalent CO2 concentration. Greenhouse gases tend to remain in the atmosphere for many years (see Table I) and consequently are well mixed. They continue to affect the climate long after initial emissions and later stabilization of atmospheric concentrations.
Aerosols can alter the climate by changing atmospheric albedo. These fine particles absorb and reflect solar radiation and alter cloud properties. Sulfate aerosols from fossil fuel emissions and smelting tend to have a negative effect on radiative forcing and thus cool the climate. Current estimates of direct radiative forcing are _0.5 W m_2 due to aerosols compared to 2.45 W m_2 due to greenhouse gases. Unlike greenhouse gases, aerosols are very short-lived in the atmosphere and therefore are not well mixed and respond rapidly to changes in emissions.

Ways To Save Energy

2010-11-02T19:14:00.000-07:00

Ways To Save Energy
With climbing fuel costs, massive unemployment, and pollution problems faced by many large cities, most Americans have more than one reason to save electricity. Contrary to most beliefs, homeowners don’t need to invest in expensive solar energy systems or residential wind turbines to save significantly on electricity costs. Most people can reduce their electricity bill dramatically by implementing these simple energy conservation techniques.

Heating and cooling are by far the highest users of electricity in the average household. This should be your first line of defense when tackling high energy bills. Installing a programmable thermostat to control the temperature of your home can be a great low cost method to reduce your energy consumption dramatically.A programmable thermostat will allow you to automatically raise your home’s temperature in the summer by a few extra degrees while everyone is scheduled to be away. By the same token, you can use a programmable thermostat to lower the temperature a few extra degrees while everyone is away in the winter. The great thing about a programmable thermostat is you can set it to bring your home back to the normal temperature just before everyone is scheduled to be back home.
The washer and dryer are two other large energy consumers in the average American home. Remember to wash and dry full loads to minimize the use of these appliances. You should also consider swapping to the latest low energy models if your current set is more than a decade old. The latest models have all sorts of new features that not only reduce electricity consumption, but also reduce the water consumption as well.
The kitchen is another room that uses a lot of electricity. Purchase a small toaster oven and use it as much as possible. Cooking meals in a toaster oven uses significantly less electricity than a full size oven.Let your dishes air dry in the dish washer instead of using the dry cycle, and always run this appliance with full loads only.
Compact fluorescent lights are another low cost method of saving significant amounts of electricity. Most CFL bulbs are reasonably priced, have a long life span, and give an equivalent amount of life as a traditional incandescent bulb. Yet they use only a fraction of the electricity as a standard bulb. For less than the cost of a dinner for two, most people can outfit their entire home with these low energy light bulbs and save a bundle.

You should implement all of these low cost techniques before considering more expensive strategies that involve turbines and solar panels. Most people will find they can reach their energy goals without the need of these more expensive and complex alternatives. Lower your electricity costs with these easy to implement low cost techniques.

Genetics

2010-11-02T19:03:00.001-07:00

At the beginning of the 20th century, the life sciences entered a period of rapid progress. Mendel’s work in genetics was rediscovered in 1900, and by 1910 biologists had become convinced that genes are located in chromosomes, the threadlike structures that contain proteins and deoxyribonucleic acid (DNA). During the 1940s American biochemists discovered that DNA taken from one kind of bacterium could influence the characteristics of another. From these experiments, it became clear that DNA is the chemical that makes up genes and thus the key to heredity.
After American biochemist James Watson and British biophysicist Francis Crick established the structure of DNA in 1953, geneticists became able to understand heredity in chemical terms. Since then, progress in this field has been astounding. Scientists have identified the complete genome, or genetic catalog, of the human body (see Human Genome Project). In many cases, scientists now know how individual genes become activated and what effects they have in the human body. Genes can now be transferred from one species to another, side-stepping the normal processes of heredity and creating hybrid organisms that are unknown in the natural world.

Why Do Teenagers Drink Alcohol?

2010-11-01T21:47:00.000-07:00

Why do teenagers drink alcohol? And what do they find so good about it?

Teenagers, like adults, drink alcohol for many different reasons, although some of them are different for teens. Your question is on teens and so I'll restrict my answer to that population.
Teens are more likely to start experimenting with drinking if they have parents who drink, if they have friends who are also drinking, and if their parents don't give them clear messages about not drinking outside the house (if they are allowed to drink some wine with dinner, for instance).
Also, alcohol is a powerful drug and changes how you feel. Some of the initial sensations at lower blood alcohol levels are pleasant and it is this sensation that many teens, as well as adults, seek.
Alcohol is a central nervous system depressant. So if you're tense or uptight, drinking some alcohol will, at least initially, reduce some of that tension and help you "chill out."
There are many other reasons why teens drink but to answer in depth would take an entire book. If you're concerned about some of your friends' drinking, consider talking with an adult in whom you can confide.
Also, if you yourself are a teen, consider attending Ala-teen. It is a 12-step group for teenagers who are concerned about other's drinking. They have a lot of literature and discussions about the dynamics of drinking and what you can do to help yourself as well as the drinker.
Whatever you do, don't drink anything and drive. The risk of being in a fatal crash is much higher at much lower blood alcohol concentrations (BACs) for drivers under 21 years of age. Here's a graph that shows the risk by age and BACs).

If you're a parent reading this, there's new data (May, 2010) on parental attitudes and teen drinking at Rather than paraphrase their conclusions I've cut and pasted them here:
Significant relationships were found between young people's drinking behaviors and perceptions of risk and protective factors in the family environment. Parental monitoring was strongly associated with family closeness and appeared to form one part of a parenting style of more general communication and regulation of children's behavior.
Findings support the need for alcohol misuse prevention interventions which address risk and protective factors within the family setting. Timing of such prevention work should be related both to the development of family relationships and the age at which young people begin drinking alcohol.

The Relationship betweenTeenage Motherhood and Marriage

2010-10-26T20:29:00.000-07:00

Teenage childbearing is associated with many adverse consequences for teen mothers, their families,
and children. Many of the negative consequences for teen mothers are due to the disadvantaged
situations in which many of these girls already lived before having a teen birth. While the disad-
vantaged backgrounds of most teen mothers account for many of the burdens that these young women
shoulder, having a baby during adolescence often restricts economic and educational opportunities, and
these disadvantages tend to be passed on to the next generation. Children born to teen mothers are often
worse off than children born to older mothers.1 They are at higher risk of poverty, low educational attain-
ment, problem behavior, early sexual activity, and becoming a teen parent themselves.2–4 Marriage, or
more speciﬁcally, the absence of marriage, helps explain this cycle of disadvantage.
Many family-related factors affect how children fare and develop over time, and marriage is one of them.
Research suggests that children do best when they are raised by two parents who have a stable marriage.5
Yet only 20 percent of teen births occur within marriage ,9 and teen pregnancy itself is associated with a
lower likelihood of marriage. Teen mothers are unlikely to marry the biological fathers of their children,
and those teenage mothers who do wed often end up in unstable marriages.6,7 For their part, the unmar-
ried fathers are less likely to be involved in their children’s lives, and reduced paternal involvement is
associated with lower child well-being.8 For all of these reasons, helping more women reach adulthood
before they have children would go a long way toward ensuring that more children grow up in stable,
married families. And considering the large body of research on the beneﬁts to children of growing up in
such families, the link between reducing teen pregnancies and improving overall child well-being is clear.
By khagendra Acharya

Bursting glacial lakes in Nepal

2010-10-26T01:37:00.001-07:00

For the people of Nepal, the threats of global warming are not something they fear for the future, but something they face right now. “Glaciers are rivers frozen in time and time is running out for Nepal's glaciers,” says Ang Tshering Sherpa, the president of the Nepal Mountaineering Association and the Union of Asian Alpine Associations. He is trying to turn the world’s attention to his country’s glacial lakes, which are threatening to burst and cause massive destruction, including the trail to Mount Everest

Five-Letter Words

2010-10-26T01:14:00.000-07:00

As I shoveled the last bite of spaghetti into my mouth, I heard a voice from the next room, “Come on, Tracy. I want to teach you some five-letter words tonight.”

“Okay, Daddy.” I skipped into the family room and my father scooped me into his lap, a pen and paper in hand.

“I’m going to write some words down, and I want you to pronounce them, all right?”

“Okay.” I kissed him on the cheek and waited excitedly for the words to

form on the page. Nights with my parents teaching me words were the highlight of my day; and little did I know they would be the most important lessons of my life.

Ever since I learned to read I have been in love with the English language. Words are my passion, and I have been writing everything from fiction to poetry since I could first form sentences. When I started preschool, I began reading books on my own. My teacher was impressed and allowed me to read to the class. My favorite books in elementary school included The Chronicles of Narnia and some of Stephen King’s shorter novels, among hundreds of others.

My parents always assumed that I would graduate at the top of my class. They were extremely proud that I was so interested in school. I was usually the first to finish assignments and would help others who were struggling. One thing that has been consistent in my life is my dream to become a teacher, and I believe it may have stemmed from the satisfaction I received from helping classmates.

Around seventh grade, my outlook on school changed. Although I maintained my love for words, I became moody and rebellious, refusing to work hard. Instead, I would sneak my own books into school and read them during class. Because of my attitude, my grades suffered.

Regrettably, I did not realize the repercussions until it was too late to erase the damage. It was difficult for me to understand the importance of school, and I am really sad that I wasted four years of my academic career. Due to dropping grades, freshman year I was grouped with the lazy, unmotivated students who hated reading (instead of those who were more like me: stimulated from the get-go and ready to learn). But instead of realizing that I was misplaced, I fell hard, telling myself, “Just wait until college. I will do all of my work then because I’ll be doing what I love every day.”

I wish I had known that this attitude would hurt me in the end, but I hope it does not cost me admission to college. While I don’t expect to be chosen over a student with an immaculate transcript, I hope that if I am compared to a student with a similar transcript, I will shine due to my passion and sincere promise of success.

I firmly believe I will succeed as a high school English teacher. English has always been my forte, and I understand how to deal with “slackers” because I am able to empathize with them. I want nothing more in life than to teach students the wonders of literature so they can reach their potential. I know I can succeed in college – it’s what I have been waiting for my whole life. Now that it is approaching, I would like the chance I feel I deserve.

My father’s lessons have enabled me to succeed and I hope they will follow me forever. Those five-letter words have had a great impact on my life, allowing me to “learn,” “dream,” “trust,” and hopefully “teach” someday.

I have the potential and the enthusiasm to succeed as an English major. It is what I have been working toward ever since those days of my parents’ teaching, and I eagerly look forward to what college has in store.

Optimism Comes with Age

2010-10-24T19:39:00.000-07:00

People tend to see the glass half full more frequently as they age, new research indicates.

Researchers showed test subjects virtual faces portraying sadness, anger, fear and happiness.They used eye-tracking technology to record which faces the subjects looked at and for how long.

Test subjects age 18-21 focused on the fear faces. Those 57 to 84 zeroed in on the happy faces and avoided the angry ones.
The participants were screened for cognitive ability—all were sharp.
What's it mean? Perhaps with their time on Earth getting shorter, people tend to focus on things that make them feel good now, the researchers figure. Whatever the reason, they seem motivated to avoid focusing on negative information.
"The study suggests that the way individuals in late life process information enables them to stay on an even emotional keel and feel good," said study leader Derek Isaacowitz of Brandeis University. "By focusing more on positive things and avoiding negative ones, older adults are able to maintain emotional resilience, which becomes acutely important in the face of dwindling time."

Teens and Sex

2010-10-23T19:31:00.000-07:00

Why teens start having sex in the first place. Environment, age of partner and perceived family support may affect young people's decisions to have sex.

While the media bombards us with alarming statistics about the number of teenagers having sex, few reports shed light on what might encourage teens to become sexually active in the first place. Three studies offer some insight into sexually active teens: environment, age of partner and perceived family support may affect young people's decisions to have sex.

In a study presented at a meeting of the American Public Health Association (APHA), researchers at the University of Kentucky followed 950 teenagers at 17 high schools in Kentucky and Ohio from 9th to 11th grades. They found evidence that teens who have intercourse tend to think their friends are too, even if they're not. "You're 2.5 times more likely to have sex by the 9th grade if you think your friends are having sex -- whether or not they really are," says Katharine Atwood, assistant professor at the Kentucky School of Public Health. Plus, teens tended to overestimate how many of their friends were sexually active. Only 33 percent of kids in the study had had sex by the 9th grade, but 31 percent said that most or all of their friends had had sex. "If you can persuade them that fewer are having sex than they think," she says, "that can have a significant impact on their behavior

Among young girls, a partner's age is a risk factor for sexual activity. "The younger the girl is at the age of first intercourse, the more likely she is to have a much older partner," says Harold Leitenberg, Ph.D., a professor of psychology at the University of Vermont. His study, published in the Archives of Sexual Behavior, found that of 4,201 girls in 8th through 12th grades, those who lost their virginity between ages 11 and 12 tended to have partners five or more years older. For girls who had sex later in adolescence, the partner's age disparity was much smaller. Early sexual initiation was also associated with a number of behavioral problems. "Ignoring the age of the partners, the earlier a girl was when she first had intercourse, the greater her risk of suicide attempts, alcohol use, drug abuse, truancy and pregnancy," Leitenberg says

The good news is that while teen sex may not be wholly preventable, the health risks it involves can be reduced through communication within the family. More research presented at the APHA meeting showed that frequent parent-child discussions about sex and its dangers may prevent teenagers from engaging in risky sexual behavior. Researchers at Emory University questioned 522 sexually active African-American adolescents about the openness and support that their families provided. Adolescents who felt that their families were more supportive were less likely to have unprotected sex, and thus were at a lesser risk for pregnancy and disease.

"The Importance Of Solar Energy Advantages"

2010-10-23T02:04:00.000-07:00

It has always been obvious that the earth is capable of producing a lot more energy than we think. In fact, most of the fossil fuels are depleting, and some people are worried about where our energy is going to come from when the inevitable happens.

However, there is a way that each of us can get the energy that we need, with little or no trouble. It is called solar energy advantages, and if everyone used it, there would be not need to ever use any other types of resources.

How Does It Work

There are many ways that solar energy advantages can work for you. First of all, the easiest way for you to take advantage of solar energy advantages is to install solar panels on your home. You can easily install these on your roof or put them in when you build a new house.

The only thing that might take a little doing is making sure that the home is wired to understand the solar energy advantages and where it is coming from. You will need to install, as well, a generator that can harness the solar energy advantages and turn it into usable power.

After you have made the installations, you don't need to worry about using your solar energy advantages only when the sun is out. First of all, the panels will catch the energy from the sun, even when it is overcast.

Also, the panels will catch much more energy than you can use in a day, so the energy is converted and stored in the solar energy advantages generator. This means that you can use it on your own, during the night and other very stormy or cloudy days.

One of the best things about using solar energy advantages is that you are doing your part to help out the earth. If everyone was to use solar energy advantages, our dependence on other types of energy would be completely gone and we'd find ourselves in a much cleaner and happier world.

It might be expensive to install solar energy advantages panels and to convert the energy at first, but once you have the system up and running, it means that you no longer have to pay for any of your electricity or even your heat. Imagine not having those bills to pay.

Also, the best thing about using solar energy advantages is that it is excellent for the earth, and if you have enough panels, you will make enough energy to actually sell some back to the electrical companies. Imagine being able to do that!

Are We Caring For The Environment?

2010-10-23T01:48:00.000-07:00

Environmental issues are becoming increasingly important worldwide, and we all have a duty to do our bit to protect our future by being as ‘green’ as possible. As we develop a furniture making business we must realise what impact we are having on the environment, and what we can do to keep carbon emissions to a minimum, as well as recycling wherever we can.

There is however, a compromise to be reached between manufacturing efficiency, affecting product cost, and what clients are willing to pay for the end product.

Before the industrial age, furniture was handmade. Trees were being cut down, planked into boards, air dried and turned into furniture all with the use of hand tools. It took two men (one of them stood in a pit) with a long saw hours to convert a tree trunk into boards, which now takes minutes with the right machine, one man with the skill to use it, and a little petrol, diesel or electricity (and hopefully gas conversions will be coming soon). The question is whether the end user is willing to pay the wages for two men to saw the wood up or pay a great deal less but put some carbon into the atmosphere?

Since the industrial revolution, we have developed machinery to speed the making process up, to a stage where the human hand does not even come in contact with wood (if indeed ‘real’ wood has been used). Thankfully, we are not, nor will we ever will be in this market. Our machines are not that specialised and we use our hand skills to make a solid piece of furniture that will become an antique. However, our woodworking machines still use electricity, which is not as ‘green’ as doing it all by hand. Our clients would not pay for labour intensive furniture. Even places such as China and India are getting away from the cheap labour methods of production, and are beginning to use more advanced mechanisation as their countries develop. This, at the same time as cutting costs to the consumer, also increases profits for the manufacturer and/or retailer.

We have to be economical (note ‘eco’) with electricity and fossil fuels without being ridiculous. Do we use a horse and cart to deliver a new four poster bed? Or do we use diesel or gas in low emission vehicles, combining deliveries to several customers, so that we are on the road as little as possible?

Customers are asking for beeswax or natural oil finished four poster beds, which is more environmentally friendly than pre-catalyst lacquers. The latter does give better protection against heat and water, but does have an impact on the environment by atomising (sprayed on) chemicals into our atmosphere. One solution that polish manufacturers are working on are water bourn lacquers, not solvent (cellulose for pre-catalyst) lacquers, but at present, we have found the ‘greener’ polish is less acceptable to the customer as the colour does not look as natural when used to produce an antique or reproduction finish.

As a business seen as consuming trees furniture makers may not seem very ‘green’, but by using locally grown timber from sustainable sources we can be as environmentally friendly as possible. Government funded schemes and grants have been introduced in parts of the UK encouraging and aiding the regeneration of local woodlands, and promoting the use of local materials from properly managed woodland, rather than using foreign hardwoods from rain forests. Virtually all of our furniture orders are made from local oak and ash, with hardly any orders coming in for mahogany, a great difference from twenty years ago. Customers are quite rightly concerned with where the timber is coming from, and mahogany like many other foreign hardwoods are out of fashion for the foreseeable future.

The Wood-Mizer sawmill can be used, and as the name suggests, has been developed to get the most out of the raw material with minimum waste. The bark and sapwood from the outside of the tree is dried and cut up for firewood, and sold locally. Small offcuts from the workshop are cut up for kindling wood, and we are at present trying to turn wood shavings and dust into winter fuel to keep us warm.

To save our ecosystem means we need, and are taking responsibility of our personal and business activities. By adapting our actions accordingly we do our share of planet saving, while maintaining a good quality, reasonably priced product that our customers are happy with, and one must remember that happy customers keep companies in business

Science for Teens

Click on desired planet and study our Solar System Enjoyingly

Study projectile Motion Graphically

Genetics

Properties of genes:

1) Each gene occupies a specific position in a specific chromosome. The position is called locus of the gene. Genes arrange in linear fashion.

ii) Deoxyribose sugar: The deoxyribose sugar in DNA is a pentose, a five-carbon sugar. Four carbons and oxygen make up the five-membered ring. It has the chemical formula C5H10O4.

XAVIER INTERNATIONAL COLLEGE

Ghale Gaun

Views of Ghale Gaun

Ghale Gaun(lumjung)

What Teenage Love is

NASA Finds Fresh Evidence of Water on Mars

Peer Pressure and Teen Sex

An Inconvenient Truth: Global Warming

Technology

Energy from Heat

The Greenhouse Effect

Ways To Save Energy

Genetics

Why Do Teenagers Drink Alcohol?

The Relationship betweenTeenage Motherhood and Marriage

Bursting glacial lakes in Nepal

Five-Letter Words

Optimism Comes with Age

Teens and Sex

"The Importance Of Solar Energy Advantages"

Are We Caring For The Environment?

ii) Deoxyribose sugar: The deoxyribose sugar in DNA is a pentose, a five-carbon sugar. Four carbons and oxygen make up the five-membered ring. It has the chemical formula C₅H₁₀O₄.