Diploiddominant

Diploiddominant, or diploid-dominant, describes a life cycle in which the dominant, multicellular stage is diploid. In such organisms the diploid phase is the primary body form, while the haploid phase is reduced to the production of gametes or to a brief, largely non-morphological phase. This pattern is characteristic of animals and many land plants, particularly the sporophyte-dominant lineages, where the sporophyte is diploid and the gametophyte is haploid but often less conspicuous or even microscopic.

In diplontic life cycles, fertilization creates a diploid zygote that develops into a multicellular diploid organism; meiosis later produces haploid gametes. The haploid stage is thus non-dominant and generally incapable of prolonged independent growth. The advantage of diploidy includes masking deleterious recessive mutations and facilitating genetic recombination through meiosis.

In plants, the term is often used in the context of sporophyte-dominant life cycles (as opposed to haploid-dominant bryophyte lineages). In gymnosperms and angiosperms, the conspicuous plant body is diploid, while the haploid components—pollen and the embryo sac—are microscopic and short-lived, serving reproductive roles rather than forming lasting bodies. In animals, the entire organism is diploid, with haploid gametes formed for reproduction.

Limitations: the boundary between diplontic and haplo-dominant life cycles can be blurred in groups with complex life cycles or reduced haploid stages, and some algae exhibit alternative patterns. See also haplontic, diplontic, life cycle, sporophyte, and gametophyte.