what is a recessive allele

A recessive allele is a type of allele that does not affect an individual when present on its own. Two copies of the allele need to be present for the phenotype to be expressed. In humans, individuals inherit two versions of each gene, known as alleles, from each parent. In the case of a recessive trait, the alleles of the trait-causing gene are the same, and both (recessive) alleles must be present to express the trait. Recessive alleles only show their effect if the individual has two copies of the allele (also known as being homozygous). For example, the allele for blue eyes is recessive, so to have blue eyes, an individual needs to have two copies of the ‘blue eye’ allele.