Following is an in-depth exploration of genes, chromosomes, etc.

To understand stem cells, telomeres, and The Human Genome Project (as well as other areas of biotechnology) it is important to have a basic knowledge of genes, chromosomes, the genome, DNA, and their relationship. A concise tutorial follows.

Genes not only determine inherited characteristics such as height or hair color, but by regulating proteins in daily life (enzymes and hormones for example are proteins), they affect virtually every function in our bodies. This includes keeping the heart beating, digestion of food, movement of muscles. Genes are arranged along longer strands called chromosomes.

The genome is the complete set of genes and chromosomes that make up all of the genetic characteristics of a particular species. The word “genome� derives from the words “gene� and “chromosome.� Just about every one of your cells contains your entire genome within it -- a set of all your genes (about 20,500), laid out on 23 pairs of chromosomes

The largest chromosome, chromosome 1, contains about 8000 genes. The smallest chromosome, chromosome 21, contains about 300 genes. The genes in each pair of chromosomes are similar but not identical. Your genome is the full set of instructions for your unique self. These instructions and the knowledge of how they work, could, in various ways someday be used to help maintain constant, optimum health.  

Genes and chromosomes are made of DNA (a chemical). DNA is in the form of a double helix or spiral. The information in DNA is stored as a code, also known as the genetic code, made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.

Total human DNA (comprising the entire genome) consists of about 3 billion bases (letters), and more than 99 percent of those bases are the same in all people. By contrast, the genome for the smallpox virus is about 185,000 bases long.

All living things are made up of DNA, represented by the letters A,G,C and T in a particular sequence, which determines the characteristics of that exact species, so the four possible “letters,â€� which form in groups of three, might be AAT, followed by CGT, followed by TGA, and so on.  

If all the DNA in your body was put end to end, it would reach to the sun and back over 600 times (100 trillion times six feet divided by 92 million miles).
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