Glossary of Relevant Genetic and Molecular/Cell Biology
The basic physical and functional unit of heredity; made up of DNA, they act as instructions to make proteins. There are about 20,000–25,000 genes in humans, with size varying from a few hundred DNA bases to more than 2 million bases. Most genes are the same in all people; less than 1% differ. Each person has two copies of each gene, one inherited from each parent. Each chromosome contains many genes.