In humans, the chromosomes occur in pairs and a typical somatic cell would contain 23 pairs of chromosomes in the nucleus. Each of these pairs has a characteristic length and banding pattern. There are two types of chromosomes: autosomes and allosomes. There are also two sets: the first set comes from the mother and the second set, from the father. Using idiograms, each chromosome may be identified one from the other based on the relative size and the banding pattern.
Chromosome 20 is a metacentric autosome. It spans almost 63 million base pairs (i.e. 2 to 2.5 % of the total DNA). It is likely to contain about 500 to 600 genes.
Some of the genes located on chromosome 20 are ADA (encoding for adenosine deaminase), EDN3 (for endothelin 3), and tTG (for tissue transglutaminase). Some of the diseases and disorders related to the genes on chromosome 20 include trisomy 20p, Alagille syndrome, fatal familial insomnia, neuronal ceroid lipofuscinosis, transmissible spongiform encephalopathy, and Waardenburg syndrome.