Genes come in pairs, and each gene in a pair may differ slightly. One gene may be dominant, and override the other gene, which is recessive. A recessive gene only has an effect if both genes in a pair are recessive. An example is eye color. Although this is not as simple as depicted here, blue is the recessive gene, and brown is the dominant gene.
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Editor's Note: This article was medically reviewed by Dana Bressette. Dana is a professor of Genetics, Nutrition, Microbiology, and Immunology at University of Phoenix and a Family Education expert.