Homozygote
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 or hemizygous for a specific gene, it means that it carries two identical copies of that gene for a given trait on the two corresponding chromosomes (e.g., the genotype is AA or aa). Such a cell or an organism is called a homozygote or hemizygote.
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).
In humans and many other animals it refers in particular to X-linked genes in males who under usual circumstances have only one X chromosome and are homozygous for all genes that are located on the X-chromosome.