Homozygous - GCSE Biology Definition

What is a homozygous genotype?

In GCSE biology an organism is homozygous when the equivalent genes in a homologous pair of chromosomes have the same alleles as each other, e.g. when they are both recessive alleles or both dominant alleles.

Every person inherits two sets of chromosomes - one from the egg cell and one from the sperm cell. Chromosomes from each set that have the same genes are called homologous chromosomes. Someone with a homozygous genotype has the same alleles on the two homologous chromosomes. For genes with dominant/recessive alleles a genotype can be either homozygous recessive or homozygous dominant.