Human Reproduction Question 24
24. Extrusion of second polar body from egg nucleus occurs:
[2019]
(a) after entry of sperm but before fertilisation
(b) after fertilisation
(c) before entry of sperm into ovum
(d) simultaneously with first cleavage
Show Answer
Answer : a
Hints & Solutions
(a) Extrusion of second polar body from egg nucleus occurs after entry of sperm into the secondary oocyte but before fertilisation. The entry of sperm into the ovum induces completion of the meiotic division of the secondary oocyte. Entry of sperm causes breakdown of metaphase promoting factor (MPF) and turns on anaphase promoting complex (APC). During gametogenesis, one cell becomes the secondary oocyte the other cell forms the first polar body. The secondary oocyte then commences meiosis 2 which arrests at metaphase and will not continue without fertilization. At fertilization meiosis 2 completes, forming a second polar body.
