Diploidia

Diploidia is a term that appears in some discussions of genetics to denote the state of having two complete sets of chromosomes, or to describe organisms that maintain two genomes within a single nucleus. It is not a standard term in formal biology; most textbooks and databases use diploidy and diploid to describe this condition.

In biology, the diploid state (2n) refers to cells containing two homologous copies of each chromosome. This contrasts with haploidy (n), in which cells carry a single set of chromosomes. In many animals and plants, somatic cells are diploid, while gametes are haploid, produced by meiosis to restore diploidy upon fertilization. Life-cycle patterns vary across groups, with some lineages spending more of their life in the diploid phase and others alternating between haploid and diploid phases.

Usage and scope: Some authors reserve diploidia for discussing contexts where two parental genomes coexist within a single nucleus, such as in certain hybrids or allopolyploids where subgenomes remain distinguishable. In such cases the organism may still be described as diploid or polyploid depending on the total number of chromosome sets, rather than as a separate category called diploidia. As a result, diploidia is largely a nonstandard or historical label rather than a formal taxonomic definition.

Measurement and examples: Karyotype analysis reveals the chromosome number, with humans typically described as having 2n = 46 and model plants like Arabidopsis thaliana as 2n = 10. Polyploidy refers to more than two chromosome sets and represents a distinct concept from diploidy.

See also: Diploidy, Haploidy, Polyploidy, Allopolyploidy, Dikaryon, Karyotype.