The complete supply of DNA--all the genes and spaces in between--in all the chromosomes of a species is called its genome. Except for red blood cells, which have no nucleus, the human genome is located in the nucleus of every cell in the body. There it is organized into 46 very large molecules called chromosomes; 44 are called autosomes and 2 are called the sex chromosomes.

An international collaboration known as the Human Genome Project has identified every chemical base in the human genome and has discovered that there are about 25,000 genes present.