Genetics, the study of heredity, is a broad area of science that encompasses many of today's fastest-growing fields, including molecular biology and biotechnology. Modern genetics offers vast potential for eliminating diseases, developing pharmaceuticals, increasing food production, and removing pollutants from the environment. The science of genetics also raises many important moral, legal, and ethical issues that are widely debated. Despite the need for "DNA literacy" - knowledge of the basic concepts of genetics - today's public is strikingly misinformed and undereducated about this fascinating and complex subject.

    The science of genetics was born in 1856, when an Austrian monk named Gregor Mendel performed an historic series of experiments on pea plants, thus discovering the laws of heredity. Although Mendel published a paper on his work, it was largely ignored by the nineteenth-century scientific community. Today, he is heralded as the "father of modern genetics".

    Mendel's laws of heredity described dominant and recessive traits. A dominant trait is one that is expressed even in the presence of other genes for the same trait. When symbolizing dominant traits, a capital letter is used. A recessive trait is one that is "obscured" by dominant traits, but is expressed when two recessive genes are present. When symbolizing recessive traits, lower-case letters are used.

    In the first of Mendel's experiments, a tall pea plant (TT) was crossed with a short pea plant (tt). The result of this cross was two tall pea plants (Tt). When these second-generation plants were crossed, the result was one tall (TT) homozygote, or organism with two of the same gene for a specific trait; two tall (Tt) heterozygotes, or organisms with two different genes for the same trait; and one short (tt) homozygote. Mendel concluded that tallness in pea plants was a dominant trait, and shortness was a recessive trait.


    After Mendel's experiments, little further progress was made in the understanding of genetics. Finally, in 1944, Oswald Avery discovered that DNA (deoxyribonucleic acid) was the molecule that carried hereditary information. In 1953, James Watson and Francis Crick discovered the double-helix structure of DNA. These discoveries laid the groundwork for modern genetics.

In order to fully understand the science of genetics, one must be aware that every human cell contains a nucleus, within which lie the 46 human chromosomes that determine each individual's genetic makeup. Chromosomes are made up of DNA, which in turn is made up of nucleotide bases. The DNA molecule is shaped like a twisted ladder, or double helix. The sides of this ladder are made of alternating sugar and phosphate molecules. The rungs of the ladder are made of four nucleotide bases - guanine, cytosine, adenine, and thymine. These bases, abbreviated G, C, A, and T, respectively, form pairs on the ladder to create a complete rung. Adenine only pairs with thymine, and guanine only pairs with cytosine. Therefore, the sequence of bases on one side of the ladder always predictably complements the sequence on the other side.
DNA replicates in a simple, straightforward manner. It splits down the middle, and the two separated strands of DNA use the sequences of their bases to rebuild their "other halves". This creates two identical copies of the original DNA molecule.

    In order to fully understand the science of genetics, one must be aware that every human cell contains a nucleus, within which lie the 46 human chromosomes that determine each individual's genetic makeup. Chromosomes are made up of DNA, which in turn is made up of nucleotide bases. The DNA molecule is shaped like a twisted ladder, or double helix. The sides of this ladder are made of alternating sugar and phosphate molecules. The rungs of the ladder are made of four nucleotide bases - guanine, cytosine, adenine, and thymine. These bases, abbreviated G, C, A, and T, respectively, form pairs on the ladder to create a complete rung. Adenine only pairs with thymine, and guanine only pairs with cytosine. Therefore, the sequence of bases on one side of the ladder always predictably complements the sequence on the other side.

    DNA replicates in a simple, straightforward manner. It splits down the middle, and the two separated strands of DNA use the sequences of their bases to rebuild their "other halves". This creates two identical copies of the original DNA molecule.

    DNA functions by indirectly making proteins, upon which every life process depends. Each group of three bases on a DNA molecule codes for an amino acid, which are the building blocks of proteins. DNA creates proteins by splitting down the middle, as in replication. It then directs the production of RNA (ribonucleic acid), which is similar to DNA, with the exception that it contains a different sugar and replaces the nucleotide base thymine with uracil. This complementary "messenger" RNA then transports its genetic information to the ribosomes (protein-making structures in a cell), where each group of three bases is read off by "transfer" RNA. The "transfer" RNA then collects amino acids that correspond to the three-base code, forming a protein chain.

    Protein synthesis is a significant focus of biotechnology, especially in medical and pharmaceutical applications. Many researchers study abnormal, disease-causing proteins and enzymes, hoping to find the DNA mutation responsible for the abnormality. Once the problem is found, gene therapy - the introduction of normal genes into patients with problematic DNA mutations - becomes a possibility. Also, alteration of genes in germline cells (eggs and sperm) can eliminate genetic diseases forever.

    Other uses of genetics in the pharmaceutical industry involve genetic engineering - the process in which genes from one organism are introduced into another organism. Genes that produce proteins, enzymes, and hormones have already been engineered into bacteria, which then produce massive amounts of the desired product. For example, this technique is used to produce large amounts of insulin for diabetics.

    Genetics can increase food production in many ways. Genes that allow plants to grow in poor soil or to resist disease, bad weather, and pest damage can be engineered into various important crops such as corn, wheat, sugar, and cotton. This could drastically cut down on pesticide use and crop loss due to inclement weather. Genes that increase the yield of such crops can also be introduced - a technique already used on cotton plants. In addition, livestock can be genetically engineered to produce more meat, to reproduce more often, or to survive in extreme climates.

    Genetics can also help to remove pollutants from the environment. Bacteria that metabolize oil have already been used in cleaning ocean oil spills. Bacteria and plants can be induced to take in heavy metals from contaminated soil and water. The organisms - and their collected pollutants - would then be removed from the area and disposed of. Bacteria can also be engineered to monitor the degree of environmental pollution; degrade chemically inert pollutants; extract and process ores safely and inexpensively; and generate environmentally friendly ethanol fuels that could provide a good substitute for oil.

    The science of genetics, at times controversial because of the moral and ethical issues it involves, also holds great promise for the future. The general public needs to be educated to become more "DNA literate"* - their enhanced understanding of the science of genetics is the key to its future uses. Almost breathtaking in the scope of its potential applications, genetics, biotechnology, and molecular biology - when used responsibly - will make valuable contributions to human society as a whole.

*The phrase "DNA literacy" was first used in an editorial in the British medical journal Lancet in 1989. The concept was expanded upon in The Book of Man, by Walter Bodmer and Robin McKie.

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Created by Kate Stafford and Michael Mannor for ThinkQuest.
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