Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Population Genetics and Alleles
Name: Robert
Status: Educator
Grade:  9-12
Location: Outside U.S.
Country: Canada
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.

Click here to return to the Molecular Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory