DNA - DNA is a molecule which encodes genetic information. It is a long, coiled, double-stranded chain of interlocking base-pairs called a double-helix. There are four types of bases in DNA: A (adenine), T (thymine), G (guanine), and C (cytosine). The order of the bases in a DNA strand, called the sequence, creates a code for information: the DNA code 'ATC' has a different meaning than the code 'TCA,' and so on. Each cell is equipped with special machinery used to read the sequence and use the information encoded.
The Human Genome Project decoded three billion letters of human DNA, providing a draft of the genome. The next major challenge will be to determine the function of genes and discover how defects in their sequence give rise to human disease.
Understanding gene function is the key to understanding disease.
A gene is a section of the DNA strand that carries the instructions for a specific function. For example, the 'globin' genes contain instructions for making the hemoglobin protein, which is the protein which allows our blood to carry oxygen throughout the body. Humans have about 50,000 different genes, which work together in complex ways to control much of what our bodies do. While we all have the same genes, there are different versions of many genes, called alleles. For example, while most people have genes which give them pigmented (coloured) eyes, there aremultiple alleles for specific eye colors. Each person has particular combination of alleles for eye color, for hair color, etc., which makes him or her genetically unique.
