What is anisogamy What form of selection caused it to evolve

What is anisogamy? What form of selection caused it to evolve?

Solution

The compatibility of gametes is an utmost requirement for fusion of two gametes from male and female to generate a viable product. However, in some exceptional cases, anisogamy might take place. Anisogamy is defined as fusion of two otherwise incompatible gametes to generate a viable offspring/product. These two gametes are not compatible to each other in genotypic or physical terms but can fuse to generate a product. Undoubtedly, this fusion product will be comprising of chromosomal abberations which will be represented in its phenotype as well. However, modern organisms have been evolved with the capability of generating a viable fertilized product even after fusion of two physically incompatible and dissimilar gametes. Fertilization of a large non-motile egg by a small motile sperm in animals and humans is a typical example of anisogamy. Here, the physical appearance of the two gametes is completely different and visibly incompatible to each other but they fuse to form a fertile and viable organism.

Genetically, anisogamy has played a crucial role in selection. It can be noted that the female gamete or ovum is very large in size and hence comprises of a huge amount of resources which will be directly utilized by the developing fertilized egg. However, the male gameter or the sperm is physically very small in size and contains no reservoir of resources which can be useful for the developing fertilized egg. In this scenario, the only mode of selection of the male gamete is the superiorness of the genetic content is contains. The better is the genetic vigour of the sperm, the more are the chances for fertilization. This is why a huge amount of sperms are produced by males while only a single of very few eggs are produced by females. This is a mode of genetic selection in higher organisms which has indirectly added up to generate variation and enhanced survivability.