Explain the stages of fertilization from sperm binding to implantation, including the role of zona pellucida, cortical reaction, and formation of the blastocyst.
Answer
Sperm binds to zona pellucida, triggers cortical reaction preventing polyspermy, fertilizes oocyte forming zygote, cleavage leads to morula, then blastocyst forms with inner cell mass and trophoblast, which implants into endometrium.
Step-by-step solution
- Sperm binds to the zona pellucida of the oocyte.
- Binding triggers the cortical reaction, releasing cortical granules and preventing further sperm entry.
- Pronuclei from sperm and oocyte merge to form a zygote.
- Zygote undergoes cleavage divisions producing a morula.
- Morula develops a fluid cavity to become a blastocyst with inner cell mass and trophoblast.
- Trophoblast cells invade the endometrium, leading to implantation of the blastocyst.
Common mistake: Assuming sperm penetrates without cortical reaction
Concept tested: Fertilization and early embryonic development
Published · How this solution was prepared and checked
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