Developmental Biology: Fertilization · Gametes and Sperm-Egg Recognition
How sperm and egg are built for their roles, and how they find, recognize and fuse with each other.
Try 3 questions
1. Why is an egg cell so much larger than a sperm cell?
- It has many copies of each chromosome
- It stores supplies for early development
- It must resist the pressure of body fluids
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Answer: It stores supplies for early development
The egg is stocked with yolk, ribosomes, mitochondria and maternal mRNAs that run the embryo's first divisions before its own genes switch on.
2. In a sperm cell, what is the main job of the mitochondria packed into the midpiece?
- Powering the beating of the tail
- Supplying mitochondria to the embryo
- Digesting the egg's outer coat
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Answer: Powering the beating of the tail
The midpiece mitochondria make the ATP that dynein motors in the flagellum use; in humans the sperm's mitochondria are destroyed after fertilization.
3. Your mitochondrial DNA almost certainly came from which parent, and why?
- Your mother, because sperm mitochondria are eliminated
- Your father, because sperm mitochondria are more active
- Both parents equally, mixed at fusion
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Answer: Your mother, because sperm mitochondria are eliminated
Sperm mitochondria enter the egg but are tagged and destroyed early on, so mitochondrial DNA is inherited from the mother.
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