Tuesday 20 September 2016

homework - Does Human Female Meiosis II occur after fertilization with sperm?



I am reading the answer and I am getting confused by the sentence:



At the end of meiosis I females have two daughter cells and meiosis II only occurs if and when fertilization occurs by a sperm cell.



The clause suggests me that meiosis II starts after the sperm has ignited the fertilization process in female: I do not know how that exactly works.


Wikipedia says:



The process of fertilization involves a sperm fusing with an ovum.



So female meiosis II must happen before the sperm fuses with the ovum. Sperm must ignite some process in female that puts female meiosis II going on before sperm can fuse with egg. Is that right? How is that going to happen?




Answer



Primary oocytes are formed prenatally and reain suspended in prophase of meiosis I for years until the onset of puberty. An oocyte completes meiosis I as its follicle matures (during ovulation) resulting in a secondary oocyte and the FIRST polar body. After ovulation, each oocyte continues to metaphase of meiosis II. Meiosis II is completed only if fertilization occurs, resulting in a fertilized mature ovum and the second polar body.


So in short, the egg is stuck in metaphase II until fertilization.


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