heterozygous

Describing an individual that has been formed either from gametes possessing contrasting alleles of a single gene or from gametes differing in the arrangement of genes (see inversion). If only one of the alleles is expressed in the phenotype, then that allele is described as dominant, and the masked allele as recessive. Heterozygosity may be inferred from the failure of an individual to breed true for the characteristic under investigation. Compare homozygous.