Only about 3 percent of the human genome is actually used as the set of instructions. These regions are called coding regions, and they are scattered throughout the chromosomes.

A coding region contains genes. A gene is a unique DNA sequence within a chromosome that ultimately directs the building of a specific protein with a specific function. Close to each gene is a "regulatory" sequence of DNA, which is able to turn the gene "on" or "off." There are at least 35,000 genes in the human genome, and there may be more.

Scientists can find no function for most of the remaining 97 percent of the genome - yet! These regions are called noncoding regions.