What does homozygous mean?
Homozygous is a genetics adjective describing an organism, cell, or genotype in which the two copies of a particular genetic locus carry the same allele. In a diploid organism, the two copies are located at corresponding positions on the homologous chromosomes inherited from the two parents. A person, plant, or animal may therefore be homozygous for a specific variant, meaning that both copies carry it. The term is especially important in the analysis of inheritance because homozygotes transmit a given recessive allele to all their offspring. It also appears in studies of dominant and recessive traits, where a homozygous dominant genotype differs from a heterozygous one. Although related nontechnical language can sometimes suggest a person is genetically “pure,” the precise scientific meaning concerns one gene or locus rather than an organism’s entire genome.
adjectiveHaving two identical alleles for a particular gene or genetic locus. In a diploid organism, it means that the corresponding alleles on the two homologous chromosomes are the same.
- Having two identical alleles at a particular genetic locus; also used of an organism or genotype in this condition.
"The test confirmed that the patient was homozygous for the recessive variant."
"Homozygous plants showed the expected leaf colour under controlled conditions."
"The variant is rare, but the affected participant was homozygous for it."
Homozygous comes from roots meaning “same” and “yoke”: it describes alleles carrying the same genetic information on paired chromosomes.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does homozygous come from?
Homozygous was formed in the early 20th century from elements meaning “same” and “yoked” or “joined,” following the development of the related noun homozygote. It belongs to a family of modern genetics terms built on Greek roots: zygote, zygous, and heterozygous. The contrast between homozygous and heterozygous reflects the fundamental distinction between identical and different alleles at the same locus.
Related word forms
How homozygous is actually used
This is primarily a genetics term. It is usually followed by “for” when naming a variant or condition and may be paired with expressions such as “homozygous dominant” and “homozygous recessive.” Its use in ordinary conversation is uncommon.
Easily confused with homozygous
A homozygous individual has two identical alleles at a locus, whereas a heterozygous individual has two different alleles there.
Homologous chromosomes are the corresponding chromosomes inherited from each parent, while homozygous describes having identical alleles at a particular locus.