Homozygote cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. When an organism is referred to as being homozygous for a specific gene, it means that it carries two identical copies of that gene on the two corresponding chromosomes (e.g. the genotype is AA or aa).

A homozygous dominant genotype occurs when a particular locus comprises two alleles for the dominant trait (e.g. AA). A homozygous recessive genotype occurs when a particular locus comprises two alleles for the recessive trait (e.g. aa).

See also: heterozygote.