Polyspermy is the biological term for the fertilization of an egg by more than one sperm.
Understanding Polyspermy
Normally, in diploid organisms, each cell contains two copies of each chromosome—one from each parent. Polyspermy disrupts this normal process by introducing additional sets of chromosomes into the egg, creating an embryo with more than the typical two sets (diploid). This is generally not viable.
Why Polyspermy is Generally Undesirable
- Chromosomal Imbalance: The presence of extra chromosomes often leads to severe developmental problems, which typically make the embryo non-viable.
- Disrupted Embryogenesis: The precise balance of genetic material is critical for normal development. Additional chromosomes interfere with gene expression and cell division.
How Organisms Avoid Polyspermy
Various mechanisms have evolved to prevent polyspermy:
-
Fast Block:
- This is a rapid electrical change at the egg's plasma membrane.
- It prevents further sperm from binding.
- It's a common mechanism in many animals.
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Slow Block:
- This involves the release of cortical granules in the egg, which alter the extracellular matrix surrounding the egg.
- These changes create a physical barrier, also preventing more sperm penetration.
- This is a more permanent method of blocking polyspermy.
Table Summary of Polyspermy
| Feature | Description |
|---|---|
| Definition | Fertilization of an egg by multiple sperm |
| Consequences | Usually results in non-viable embryos |
| Normal Chromosome | Two sets (diploid) |
| Polyspermic | More than two sets |
| Prevention | Fast and slow blocks to sperm entry. |
Conclusion
Polyspermy, while interesting from a biological perspective, is a process that is carefully avoided by organisms to ensure proper development. It leads to nonviable embryos due to the resulting chromosomal imbalances.
