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.
