What does heterozygous mean?
Heterozygous is a genetics term describing an organism, cell, or genotype that carries two different versions, or alleles, of a particular gene. One allele is inherited from each parent, so the two copies are not identical. The term is especially important in discussions of inherited disorders, genetic variation, selective breeding, and evolution. A person may be heterozygous for one gene and homozygous for many others, so the word is normally used in relation to a specific gene or locus. It also helps explain how recessive traits recur: when two heterozygous parents each contribute a recessive allele, a child may receive that allele from both parents and therefore be homozygous for it. Although heterozygous is principally a formal scientific adjective, its contrast with homozygous makes it useful whenever the difference between matching and differing gene copies matters.
adjectiveHaving two different alleles of the same gene, one inherited from each parent. The term can also describe a genotype containing such a pair of alleles.
- Having two different alleles of the same gene, one inherited from each parent; also referring to a genotype composed of such unlike alleles.
"The plant was heterozygous for the gene that confers resistance to the disease."
"The laboratory analysis showed that the patient was heterozygous for the variant associated with the disorder."
"Most of the flowering population was heterozygous, while a smaller group carried the same allele in both copies."
Two heterozygous parents can have a homozygous child—recessive traits do not vanish; they can wait in hiding.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does heterozygous come from?
The word was formed in scientific usage by combining the Greek-derived prefix hetero-, from heteros, meaning “different” or “other,” with zygous, an adjective associated with zygotes and joined pairs. The zyg- element ultimately comes from Greek zygon, meaning “yoke,” reflecting the pairing of reproductive cells. In the resulting compound, hetero- distinguishes unlike alleles from the matching copies described as homozygous.
Related word forms
How heterozygous is actually used
This is a formal scientific term used chiefly in genetics, biology, breeding, and related fields. It normally characterizes an organism, individual, cell, or genotype at a particular gene or locus rather than serving as a general label for a heterogeneous person or thing.
Easily confused with heterozygous
A heterozygous organism carries two different alleles of a gene, whereas a homozygous organism carries two identical copies.
Heterozygous is a precise genetics term referring to allele differences at a gene, while heterogeneous more generally means varied or composed of different parts.