What does dizygous mean?
Dizygous is an adjective from genetics and embryology describing offspring — most often twins — that develop from two separately fertilized eggs. Because each twin arises from its own fertilized ovum, dizygous twins share, on average, only about half of their genes, making them genetically comparable to ordinary brothers and sisters born at different times. This distinguishes them from monozygous (identical) twins, which come from a single fertilized egg that splits into two embryos with essentially identical DNA. The word appears almost exclusively in formal and scientific contexts such as medical literature, psychology studies, and discussions of heredity, where twin comparisons are used to separate the effects of nature and nurture. In everyday conversation, speakers prefer the friendlier terms 'fraternal' or 'non-identical.' A close synonym, 'dizygotic,' occurs even more frequently in technical writing. Understanding 'dizygous' offers a precise way to talk about the biological distinction between sibling-like twins and true genetic duplicates.
adjectiveDeveloping from two separate fertilized eggs; used chiefly of fraternal (non-identical) twins, who arise from two distinct zygotes and are genetically no more alike than ordinary siblings.
- (Of twins or multiple births) derived from two separately fertilized ova, and therefore genetically distinct individuals rather than identical copies.
"The study compared dizygous twins raised apart to estimate the heritability of intelligence."
"Roughly two-thirds of all twin pregnancies produce dizygous twins."
"Because the siblings were dizygous rather than monozygous, researchers could not treat them as genetic duplicates."
Dizygous twins share a womb and often a birthday, yet genetically they're no more alike than any brother and sister.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dizygous
Dizygous derives from Greek roots: 'di-' meaning 'two' and 'zygous' from 'zygon,' meaning 'yoke,' via the biological term 'zygote,' itself coined in the late nineteenth century to denote a fertilized egg — literally a cell formed by the union of two gametes. The adjective was formed within scientific English alongside its counterpart 'monozygous,' using the same combining forms that appear in related terms like heterozygous and homozygous. Its near-synonym 'dizygotic' arose by the same route through 'zygote.'
Related word forms
How dizygous is actually used
Dizygous is a technical term used mainly in genetics, embryology, medicine, and twin research. In everyday speech, 'fraternal' or 'non-identical' is far more common. The adjective 'dizygotic' is more frequent in scientific literature than 'dizygous'; both carry a neutral, clinical register.
Easily confused with dizygous
Monozygous describes identical twins developing from a single fertilized egg, whereas dizygous describes fraternal twins developing from two separate eggs.
Dizygotic is simply a more common synonym for dizygous — both mean 'from two zygotes' — but they differ in form, not meaning.