heterozygote A diploid or polyploid individual that has different alleles (forms of a given gene) at at least one locus. Its phenotype is often identical to that of an individual that has one of these alleles in the homozygous state. (For example, the phenotype of A₁A₂ may be identical to that of A₁A₁, but different from that of A₂A₂.) If so, that allele (A₁) is said to be dominant over the other (A₂), which is said to be recessive. When there exist only 2 alleles of a gene and when one of these is dominant over the other, one may use a lower-case letter for the recessive allele; e.g., one may write Aa rather than A₁A₂. However, alleles are not always dominant one over another (see PARTIAL DOMINANCE); and often there are more than 2 alleles at a given locus (see MULTIPLE ALLELISM), especially in polyploids. Because it has two or more different alleles at a given locus, a heterozygote does not breed true.

heterozygote A diploid or polyploid individual that has alleles at at least one locus. Its phenotype is often identical to that of an individual that has one of these alleles in the homozygous state. For example, the phenotype of A₁A₂ may be identical to that of A₁A₁, but different from that of A₂A₂. If so, that allele (A₁) is said to be dominant over the other (A₂), which is said to be recessive. When there exist only two alleles of a gene and when one of these is dominant over the other, one may use a lower-case letter for the recessive allele (e.g. one may write Aa rather than A₁A₂). However, alleles are not always dominant one over another; and often there are more than two alleles at a given locus, especially in polyploids. Because it has two or more different alleles at a given locus, a heterozygote does not breed true.

heterozygote (symbol Hz) Organism possessing two contrasting forms (alleles) of a gene in a chromosome pair. In cases where one form is dominant and the other recessive, only the dominant form is expressed in the phenotype (physical characteristics). A homozygote has identical forms of a gene.

heterozygote An organism or cell that is heterozygous.