Figure 1.

A brief guide to genomics. Cancer is a disease of the genome because DNA alterations provide the biological basis of cancer. Each body cell (except for mature red blood cells) contains a full copy of the organism's genome within a set of chromosomes packed in its nucleus. The DNA double-helix is formed by four nucleotides, or bases, assembled in complementary pairs via hydrogen bonds: adenine (A) is always paired with thymine (T), and cytosine (C) is always paired with guanine (G). The gene is the basic unit of heredity and consists of a long sequence of nucleotides that encodes for the synthesis of a protein by transcription to RNA (ribonucleic acid) in the cell's nucleus, followed by translation to a sequence of amino acids in the cytoplasm. The average gene comprises several thousand bases, with wide size variation. The DNA double-helix strand wraps around a set of histone proteins, forming structures known as “nucleosomes” at regular intervals along the length of the strand (Adapted from National Human Genome Research Institute, genome.gov).