Polar body

Polar body

A polar body is a small haploid cell that is formed concomitantly as an egg cell during oogenesis, but generally does not have the ability to be fertilized.

Formation

The formation of a polar body is part of the process of meiosis in female animals. This process includes two divisions, meiosis I and meiosis II, both of which usually occur after the sperm has entered the egg but before fertilization.

Meiosis I

During meiosis I, the oocyte divides its chromosomes evenly, but distributes most of the cytoplasm to one daughter cell, forming one large secondary oocyte and one small polar body. The polar body usually dies and disappears, but sometimes can divide again.

Meiosis II

If the secondary oocyte is fertilized, it completes meiosis II, dividing its chromosomes evenly, but distributing most of the cytoplasm to one daughter cell. This forms one large ovum and one small polar body. The second polar body also usually dies and disappears.

Function

The main function of polar bodies is to ensure that the egg, and therefore the zygote after fertilization, has the correct number of chromosomes. This is achieved by removing the excess chromosomes from the egg.

See also

• Oogenesis
• Meiosis
• Zygote

References

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