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Oogenesis and fertilisation
Concepts tested here
- Completion of meiosis II
All Questions
2010 AIPMT-PRE 1 question
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The second maturation division of the mammalian ovum occursThe first meiotic division of the primary oocyte is completed in the tertiary follicle just before ovulation, forming a large secondary oocyte and a tiny first polar body.
The secondary oocyte begins the second meiotic division but is arrested at metaphase II, and it is released in this state at ovulation.
The second division is completed only when a sperm enters the cytoplasm of the secondary oocyte: the entry of the sperm induces the completion of meiosis II, forming the second polar body and a haploid ovum (ootid).
Only after this do the haploid nuclei of the sperm and the ovum fuse to form the zygote.
Hence the second maturation division does not occur until after the ovum has been penetrated by a sperm.