Karyogamie

Karyogamy, also known as karyogamie in French, is the fusion of two haploid nuclei during sexual reproduction to form a single diploid nucleus. It is a key step that follows plasmogamy, the fusion of cytoplasm, in many organisms. By uniting the genetic material from the two gametes, karyogamy reestablishes diploidy and sets the stage for genetic recombination through meiosis.

In fungi, karyogamy is a central event in the life cycles of many species. After plasmogamy, many fungi form a dikaryotic stage in which two distinct nuclei coexist in the same cell. Karyogamy then occurs within specialized structures (for example, asci in ascomycetes or basidia in basidiomycetes), producing a diploid nucleus. This diploid phase typically undergoes meiosis to generate haploid spores, which can develop into new haploid individuals.

In animals and plants, fertilization involves the fusion of haploid gametes and the merging of their nuclei to form a diploid zygote; this nuclear fusion is conceptually equivalent to karyogamy, though the term is more commonly applied within the context of fungal biology. Regardless of lineage, karyogamy culminates in the formation of a single, fertilized nucleus from two parental nuclei, after which meiotic divisions may produce genetic diversity.

Etymology derives from Greek karyon (nucleus) and gamos (marriage). Karyogamy is distinct from plasmogamy and is often followed by meiosis, contributing to the genetic variation seen in sexually reproducing populations.