allele

either of a pair (or series) of alternative forms of a gene that can occupy the same locus on a particular chromosome and that control the same character; "some alleles are dominant over others"

स्थल पर विशिष्ट युग्मविकल्पी का नामकरण किया जा सके.

Consider, for the sake of illustration, two heterozygous alleles Aa and Bb which are carried in the same pair of chromosomes.