Both allogamy and xenogamy are terms used in biology to describe two types of sexual reproduction that differ in the origin of the male and female gametes involved in fertilization.
If the gametes come from the same individual, we speak of autogamy. If the gametes come from different individuals, they are called allogamy.
When talking about plants, allogamy is synonymous with cross-pollination, but cross-pollination in plants also occurs between different flowers of the same individual. And also between flowers from different individuals, but which are genetic clones.
Thus, in plants, two types of allogamy or cross-pollination are distinguished: xenogamy and geitonogamy. In xenogamy, flowers from genetically different individuals are involved, while in geitonogamy, genetically identical individuals are involved or, which at the genetic level gives the same result, different flowers from the same individual.
Allogamy, xenogamy and cross-pollination
In allogamysingamy (fertilization or fertilization) occurs between gametes of different individuals. In other words, alogmy is a type of syngamy that occurs between a sperm and an egg from different individuals.
Reproduction in humans would be a form of allogamy.
On the contrary, the autogamy It is a process of self-fertilization, it is a type of syngamy that occurs with sperm and eggs coming from the same individual. Autogamy is very common in plants and certain types of protozoa.
In the specific case of plants, fertilization or syngamy is often called pollination. Allogamy would be what is called cross-pollination or indirect pollination and includes not only pollination between different individuals, but also pollination between different flowers of the same individual.
Autogamy would be called self-pollination or direct pollination and would be self-fertilization in hermaphrodite flowers (stamens and pistils in the same flower).
In cross-pollination, as plants can reproduce asexually and give rise to genetically cloned individuals (lineages), they differentiate two types of allogamy:Xenogamy: is cross-pollination between genetically different plants or individuals. Geitonogamy: is the allogamy or pollination that occurs between different flowers but from the same individual or between flowers from different individuals but genetically the same (between clones or lineages).
Therefore, allogamy is syngamy (union of gametes) that occurs between different individuals. When gametes intervene, allogamy is a process of sexual reproduction. Autogamy is another process of sexual reproduction in which the gametes come from the same individual.
In plants, cross-pollination would be a form of allogamy, but the term allogamy is also used to refer to cross-pollination. different flowers from the same individual.
Many plants have unisexual flowers of different sex on the same plant; pollen from a male flower can fertilize a female flower on the same plant, and this would also be a form of allogamy, specifically a type of allogamy called geitonogamy.
Cross-pollination between flowers from the same individual has the same result at the genetic level as pollination between different genetically identical individuals or clones. These clones are formed by one of several methods of asexual reproduction that plants follow, and pollination between them is also considered geitonogamy.
xenogamy It would be another type of allogamy that occurs in plants when the pollen comes from flowers of another genetically different individual, never from the same individual or between clones or between the same lineage
As xenogamy occurs between genetically different individuals, it can even occur between plants of different species in some cases, the term cross-hybridization to differentiate it from simple cross-pollination.