Question

In human females, meiosis II occurs

• A. At ovulation
• B. Immediately after the sperm penetration of the secondary oocyte
• C. Immediately after the sperm penetrates the primary oocyte
• D. None of the above

Answer 1

The correct option is B Immediately after the sperm penetration of the secondary oocyte

The oocyte is arrested during metaphase II of meiosis II. This arrest is facilitated by a complex called "Cytostatic Factor" (CSF). After fertilization, the sperm induces a rise in intracellular calcium ion which activates an enzyme, Calmodulin Kinase II. This complex, through a series of phosphorylation and ubiquitination, degrades the CSF complex and in turn, activates APC (Anaphase Promoting Complex). APC will then degrades cyclins, securins and this will promote the completion of meiosis II.

So the correct option is 'immediately after the sperm penetration of the secondary oocyte'.