recessive allele, the member of a pair of alleles that lacks the ability to express itself in the presence of a dominant allele at the same locus.It is expressed only in the homozygous state. Compare dominant allele.See also autosomal-recessive inheritance.he member of a pair of alleles that lacks the ability to express itself in the presence of a dominant allele at the same locus. It is expressed only in the homozygous state. Compare dominant allele. See also autosomal-recessive inheritance.