Question Video: Recalling When Meiosis II is Completed in Females Biology • Third Year of Secondary School

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In females, when is meiosis II completed? [A] After a secondary oocyte has been fertilized. [B] When the female embryo is developing. [C] Just before the egg is released at ovulation. [D] Just after the egg is released at ovulation and before fertilization. [E] At the start of each menstrual cycle.

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Video Transcript

In females, when is meiosis II completed? (A) After a secondary oocyte has been fertilized. (B) When the female embryo is developing. (C) Just before the egg is released at ovulation. (D) Just after the egg is released at ovulation and before fertilization. (E) At the start of each menstrual cycle.

Let’s start by reviewing meiosis I and meiosis II. During meiosis I, the diploid primary oocyte divides so that half of its duplicated chromosomes go into the secondary oocyte and the other half go into a polar body. Now the secondary oocyte begins meiosis II, but it pauses before it can finish. The secondary oocyte remains paused in meiosis II until a sperm cell fertilizes it. This triggers the egg to complete meiosis II.

During meiosis II, the duplicated chromosomes are separated into a polar body and a mature ovum. At this point, the haploid nuclei of the egg and sperm are able to fuse to form the zygote. Therefore, when meiosis II is completed is given by answer choice (A): after a secondary oocyte has been fertilized.