Population Genetics and Alleles
Location: Outside U.S.
Date: October 2008
Why do dominant genes not simply cause recessive genes to
disappear from the gene pool over time?
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.
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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Update: June 2012