Allogamie

Allogamy, or cross-fertilization, is a mode of sexual reproduction that requires gametes from genetically distinct individuals. It contrasts with autogamy (self-fertilization) and geitonogamy (pollination between flowers on the same plant). In plants, allogamy occurs when pollen from one plant fertilizes the stigma of another, often via wind or animal vectors, leading to seed production. In animals, it describes fertilization resulting from mating between separate individuals. In fungi and some algae, allogamy denotes fertilization between genetically different mating types, a prerequisite for many sexual cycles.

Allogamy increases genetic diversity, promoting adaptation and reducing inbreeding depression, but it requires compatible partners and often more energy to locate mates or pollinators. Plants commonly employ self-incompatibility systems, dioecy, or ecological barriers to promote outcrossing; many species show mixed mating systems with both selfing and outcrossing depending on conditions. Outcrossing can be obligate or facultative, varying with factors such as pollinator availability, population density, and environmental context.

The concept is widespread in biology and underpins much of the genetic variation observed in flowering plants and many animal groups. Its study illuminates how mating systems influence evolution, population dynamics, and the balance between genetic stability and adaptability in natural communities.