Question

question 70
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which is the correct sequence of events in fertilization?
acrosomal reaction -> capacitation -> cortical reaction -> union of pronuclei
capacitation -> acrosomal reaction -> cortical reaction -> union of pronuclei
capacitation -> acrosomal reaction -> union of pronuclei -> cortical reaction
acrosomal reaction -> capacitation -> union of pronuclei -> cortical reaction -> union of pronuclei

Explanation:

• Capacitation: Sperm undergo capacitation in the female reproductive tract, which makes their membranes more fragile and allows enzymes in their acrosomes to be released.
• Acrosomal reaction: When a sperm reaches the zona pellucida (outer layer of the egg), the acrosomal reaction occurs. Enzymes are released from the acrosome (a cap - like structure on the sperm head) to help the sperm penetrate the zona pellucida.
• Cortical reaction: Once a sperm penetrates the egg membrane, the cortical reaction takes place. Cortical granules in the egg release their contents, which harden the zona pellucida and prevent polyspermy (entry of multiple sperms).
• Union of pronuclei: After the sperm enters the egg, the sperm nucleus (male pronucleus) and the egg nucleus (female pronucleus) come together and fuse, combining their genetic material.

Answer:

Capacitation → Acrosomal reaction → Cortical reaction → Union of pronuclei