The chemical factors that determine traits are called genes. With the exception of less than 1 percent of genes, the rest of the genes in people are the same.
The specific genes, which are different from one person to another and give each person special physical features, are named alleles. Each person carries a copy of genes from each parent. Made of deoxyribonucleic acid (DNA) bases, a gene can carry a couple of hundred to over two million DNA bases.
Since DNA has stored chemical information, a gene carries coded instructions for a specific protein or for performing a specific function. Each person is said to have 20,000 to 25,000 genes, according to the Human Genome Project.