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The Collaborative International Dictionary

anisogamy \anisogamy\ n. 1. (biology) reproduction by the union or fusion of two differing gametes (especially differing in size).


n. 1 A form of sexual bonding involving partners of unusually widely differing ages. 2 (context cytology English) Sexual reproduction involving the union or fusion of two dissimilar gametes.


n. (biology) reproduction by the union or fusion of two differing gametes (especially differing in size)


Anisogamy (also called heterogamy) is the form of sexual reproduction that involves the union or fusion of two gametes, which differ in size and/or form. (The related adjectives are anisogamous and anisogamic. The smaller gamete is considered to be male ( sperm cell), whereas the larger gamete is regarded as female ( egg cell).

There are several types of anisogamy. Both gametes may be flagellated and therefore motile. Alternatively, both of the gametes may be non-flagellated. This [which?] situation occurs in some algae and plants. In the red alga Polysiphonia, non-motile eggs are fertilized by non-motile sperm. In flowering plants, the gametes are non-motile cells within gametophytes.

The form of heterogamy that occurs in animals, including humans, is oogamy. In oogamy, a large, non-motile egg ( ovum) is fertilized by a small, motile sperm ( spermatozoon). The egg is optimized for longevity, whereas the small sperm is optimized for motility and speed. The size and resources of the egg cell allow for the production of pheromones, which attract the swimming sperm cells.