Oogamy
Form of sexual reproduction
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Through Sexual reproduction, Gamete and Animal
Occurrence
Oogamy is found in almost all animal species that reproduce sexually. There are exceptions, such as the opiliones that have immobile sperm.
Oogamy is found in all land plants, and in some red algae, brown algae and green algae. Oogamy is favored in land plants because only one gamete has to travel through harsh environments outside the plant. Oogamy is also present in oomycetes.
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Etymology
The term oogamy was first used in the year 1888. It derives from the Greek noun "oon" (ΩΟΝ = egg) and the Greek verb "gameo" (ΓΑΜΕΩ → ΓΑΜΩ = to have sex/to reproduce) and eventually means "reproduction through eggs".
Evolution
The ancestral state of sexual reproduction is probably isogamy, in which both gametes are identical, from which oogamy is thought to have evolved multiple times through anisogamy. When oogamy has evolved, males and females typically differ in many aspects. Oogamy evolved before the transition from external to internal fertilization.
In streptophytes, oogamy occurred before the split from green algae.