Here's why:
* Natural Selection: Severe effects from a dominant allele usually mean a significant decrease in fitness (survival and reproduction). This makes it unlikely for the allele to persist in a population for long periods.
* New Mutations: The dominant allele is more likely to arise as a new mutation. This means it's rare in the population and unlikely to be passed on frequently.
* Recessive Alleles: In contrast, recessive alleles can hide in carriers and stay in the population for longer, even if they have severe effects.
Example: Achondroplasia, a form of dwarfism, is caused by a dominant allele. It's relatively rare, and individuals with the condition often have shorter lifespans. This is because the severe effects of the dominant allele make it difficult for individuals to survive and reproduce.
Exceptions: While rare, dominant alleles with severe effects can persist in a population if they have some selective advantage in other contexts.
Let me know if you would like more details on any of these concepts!
