Syngamy

Syngamy is the fusion of two gametes to form a zygote, the first cell of a new organism in sexual reproduction. The term can refer to the overall process of gamete union, or more narrowly to the fusion of cytoplasm (plasmogamy) followed by the fusion of nuclei (karyogamy). In many contexts, the two steps occur in rapid succession, producing a single diploid zygote.

In fertilization, a haploid sperm and a haploid egg meet and recognize each other. Surface interactions and adhesion bring the gametes into contact, membranes fuse, and cytoplasm mixes. After plasmogamy, the haploid nuclei may remain separate for a time in some lineages (as in certain fungi) or fuse quickly to form a diploid nucleus (karyogamy). This transition restores the species’ diploid state and initiates the zygote’s development.

Syngamy occurs across a wide range of organisms, including animals, plants, fungi, and many protists. It can be isogamous, with morphologically similar gametes, or anisogamous, with distinct male and female gametes. Fertilization can be external (occurring outside the parent’s body, often in aquatic environments) or internal (within the reproductive tract or ovule in animals and plants).

Genetic consequences of syngamy include the combination of parental genomes, increasing genetic variation in the offspring. Following zygote formation, many organisms proceed through meiosis to return to haploidy in the next generation, producing gametes or spores. The study of syngamy encompasses cellular adhesion, membrane fusion, and the regulation of subsequent nuclear fusion in diverse life forms.