An allele is a variant form of a gene. Genes are made up of DNA sequences and can exist in multiple forms, or alleles, that are slightly different from each other. Each individual has two alleles for each gene, one inherited from each parent. Alleles can be dominant or recessive, determining the expression of certain traits or features in an organism. For example, in humans, the gene for hair color has multiple alleles, such as brown, blonde, or red, and the combination of alleles determines an individual's hair color.
