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Name: Robert
Status: Educator
Grade:  9-12
Location: Outside U.S.
Country: Canada
Date: October 2008


Question:
Why do dominant genes not simply cause recessive genes to disappear from the gene pool over time?



Replies:
Just because a trait is dominant doesn't mean that it will displace another trait. Dominant just means that it only takes one copy of the allele to be seen. It also doesn't mean it is the most common allele in the population. In order for a trait to disappear from the gene pool all heterozygotes also need to weeded out.

Vanhoeck

If the dominant gene does not have a selective advantage over the recessive gene, then the frequency of the dominant gene will not change. This is described by the Hardy-Weinberg Law which states that in the absence of mutation, migration, natural selection and non-random mating, the frequency of genes in a population will remain constant. Another reason is that if heterozygous individuals have a slight selective advantage over either of the homozygous types, then both genes are retained in the gene pool. This is known as polymorphism. An example of polymorphism is sickle cell anemia.

Ron Baker, Ph.D.



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