Oogamy

 ( Reproductive System ) 

Oogamy is a form of anisogamy where the gametes differ in both size and form. In oogamy the large female gamete (also known as Egg cell) is immotile, while the small male gamete (also known as spermatozoon) is mobile.

Oogamy is a common form of anisogamy, with almost all animals and land plants being oogamous.

Oogamy is found in most sexually reproducing species, including all vertebrates, land plants, and some algae. The ancestral state of sexual reproduction is believed to be isogamy, with oogamy evolving through anisogamy. Once oogamy evolves, males and females typically differ in various aspects. Internal fertilization may have originated from oogamy, although some studies suggest that oogamy in certain species may have evolved before the transition from external to internal fertilization. In streptophytes, oogamy occurred before the split from green algae.

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Occurrence Oogamy is found in almost all animal species that reproduce sexually.

Graham Bell (2019). 9781000497441, Routledge. . ISBN 9781000497441

David B. Dusenbery (2025). 9780674060210, Harvard University Press. . ISBN 9780674060210

There are exceptions, such as the opiliones that have immobile sperm.

(2010). 9780195325553, Oxford University Press, USA. . ISBN 9780195325553

Oogamy is found in all Embryophyte,

and in some red algae, brown algae and green algae.

(2025). 9780716710073, W. H. Freeman. . ISBN 9780716710073

Oogamy is favored in land plants because only one gamete has to travel through harsh environments outside the plant. Oogamy is also present in .

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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".

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Evolution

It is generally accepted that isogamy is the ancestral state

(2008). 9780080919874, Academic Press. . ISBN 9780080919874

and that oogamy evolves from isogamy through anisogamy.

Awasthi & Ashok Kumar9789325990227, Vikas Publishing House. . ISBN 9789325990227

When oogamy has evolved, males and females typically differ in many aspects. Oogamy evolved before the transition from external to internal fertilization.

In Streptophyta, oogamy occurred before the split from green algae.

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See also

• Gamete
• Anisogamy
• Isogamy

Categories: Reproductive System, Germ Cells

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