What does diploidy mean?
Diploidy is the biological state in which a cell or organism carries two complete sets of chromosomes, one set inherited from each parent. In humans, for example, somatic cells are diploid, containing 46 chromosomes arranged in 23 homologous pairs, while sperm and egg cells carry only a single set and are described as haploid. The fusion of two haploid gametes at fertilization restores diploidy in the zygote, ensuring that offspring inherit genetic material from both parents. This dual arrangement provides an important advantage: it allows organisms to carry two copies of each gene, which can mask harmful recessive mutations and supplies raw variation on which natural selection acts. The term belongs chiefly to genetics, cytology, and evolutionary biology, where it is routinely contrasted with haploidy and polyploidy, conditions involving one or more than two chromosome sets respectively.
nounThe state or condition of a cell or organism possessing two complete sets of chromosomes, one inherited from each parent. It is the normal chromosomal constitution of most somatic cells in animals and plants.
- The condition in which cells contain two complete homologous sets of chromosomes, denoted 2n.
"In humans, diploidy is maintained in nearly all body cells, each carrying 46 chromosomes."
"The fertilized egg restores diploidy by combining one chromosome set from each parent."
"Selective breeding programs often rely on maintaining diploidy to preserve predictable inheritance patterns."
Rarely pluralized; the word is almost always used as an uncountable mass noun referring to the general condition.
"Comparative studies have examined the diploidies of various plant lineages."
Every cell in your body is living proof of diploidy — carrying two full copies of your genome, one from your mother and one from your father.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of diploidy
Diploidy derives from the adjective 'diploid', formed from the Greek root 'diploos' meaning 'double' or 'twofold', combined with the suffix '-oid' indicating likeness or form. The Greek root 'diplo-' appears widely across scientific and everyday English, giving us words such as 'diploma', 'diplopia' (double vision), and, through its Latin cousin 'duplex', 'duplicate' and 'double'. The term arose in late 19th- and early 20th-century cytology, when biologists were first working out that chromosomes exist in paired sets within cells, and it became standard vocabulary as modern genetics took shape.
Related word forms
How diploidy is actually used
Strictly technical vocabulary used almost exclusively in genetics, cytology, and biology; it rarely appears in general conversation. It is typically discussed alongside its counterpart 'haploidy', which characterizes gametes such as sperm and egg cells.
Easily confused with diploidy
Haploidy is the state of having a single set of chromosomes (as in gametes), whereas diploidy is the state of having two sets.