Heterozygous - GCSE Biology Definition

What is a heterozygous genotype?

In GCSE biology an organism is heterozygous when the equivalent genes in a homologous pair of chromosomes have different alleles to each other, e.g. when one is a dominant allele and one is a recessive allele.

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 heterozygous genotype has different alleles on the two homologous chromosomes. For genes with dominant/recessive alleles a heterozygous individual will always show the dominant phenotype.