Heterozygote: A person possessing two different forms of a particular gene, one inherited from each parent. A heterozygote is also called a carrier.

For example, a woman who is a heterozygote for cystic fibrosis (CF) carries the CF gene on one of her chromosomes number 7 and the normal paired (non-CF) gene at the same position on her other chromosome 7. She is a carrier for CF but has no signs or symptoms of the disease.

A manifesting heterozygote is a person who manifests signs or symptoms of what is usually a recessive condition and ordinarily only is evident in someone who has two copies of the gene.

A compound heterozygote has two different mutant forms of a particular gene.