recessive allele

the version of a gene (see allele) whose effects are manifest only if it is carried on both members of a homologous pair of chromosomes. Hence, the trait determined by a recessive allele (the recessive trait) is apparent only in the absence of another version of that same gene (the dominant allele). The term autosomal recessive is used to describe patterns of inheritance in which characteristics are conveyed by recessive alleles. For example, Tay–Sachs disease is an autosomal recessive disorder.