What does disomy mean?
Disomy is a genetics term describing the presence of exactly two copies of a particular chromosome within a cell — the normal state for human body cells, which carry one maternal and one paternal copy of each chromosome. Although it describes the standard condition, the word is most often encountered in discussions of what happens when this arrangement goes wrong. Cytogeneticists may speak of 'uniparental disomy', where both copies of a chromosome come from just one parent, an anomaly that can cause disease if the two copies carry identical mutations or if genomic imprinting is disturbed. Disomy also serves as a reference point against which abnormalities such as monosomy (one copy) and trisomy (three copies) are defined. Formal and technical in register, the word belongs to the vocabulary of medical genetics rather than general conversation, but it captures a fact fundamental to human biology.
nounThe state of a cell or organism having exactly two copies of a particular chromosome, one inherited from each parent, as in a normal diploid cell. The term is used chiefly in genetics and cytogenetics, especially when discussing chromosomal abnormalities such as uniparental disomy.
- The presence of two homologous copies of a given chromosome in a cell, the normal diploid condition for autosomes; used especially in contrast to monosomy or trisomy.
- In uniparental disomy, the situation in which both copies of a chromosome (or a segment of one) derive from a single parent rather than one copy from each parent.
"Uniparental disomy occurs when both copies of a chromosome are inherited from a single parent instead of one from each."
"Karyotyping confirmed disomy of chromosome 15 in all cells examined."
"The embryo was screened and found to show normal disomy for every chromosome tested."
Rarely pluralized; the term usually appears in the singular even when discussing multiple chromosomes.
"The analysis identified several segmental disomies across different chromosomes."
You've probably never heard of disomy — yet it's literally the reason your cells work: two copies of every chromosome, one from each parent.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of disomy
Disomy was coined in the twentieth century within modern scientific Latin, drawing on Greek elements already established in biology. It combines the prefix 'di-', meaning 'two' or 'double' (from Greek 'dis'), with '-somy', a suffix derived from the Greek 'soma', meaning 'body', which entered English through the earlier coinage 'chromosome' ('colored body'). The same pattern produced the related terms monosomy and trisomy, denoting one and three copies respectively. Its cognates therefore include not only these sister terms but also words built on the same Greek root for body, such as somatic.
Related word forms
How disomy is actually used
A formal scientific term used almost exclusively in genetics, cytogenetics, and medical contexts; it is rare in everyday language. In clinical writing it often appears in the fixed phrase 'uniparental disomy'.
Easily confused with disomy
Trisomy refers to having three copies of a chromosome (as in Down syndrome's trisomy 21), whereas disomy is the normal condition of having exactly two.
Monosomy is the presence of only one copy of a chromosome rather than the usual two found in disomy.
Dichotomy means a division into two contrasting parts or categories, while disomy is a technical genetic term for possessing two copies of a chromosome.