(Pages 194 – 207)
6.3. Patterns of Selection: Testing Predictions of Population Genetic Theory
Selection on Recessive and Dominant Alleles
This chapter covers the mathematics behind the evolution of populations. Read the book
because I can’t explain numbers in words.
Chapter 6 (Pages 210 – 218)
Adding Mutation to the Hardy – Weinberg Analysis: Mutation as an Evolutionary Mechanism
Mutation by itself is generally not a rapid mechanism of evolution.
o For example in a population with a frequency of 0.9 for A alleles and a frequency of 0.1
for a alleles, a mutation rate of 1 per 10 000 (a high rate of mutation) would result in
frequency of 0.89991 for the A allele and frequency of 0.10009 for the a allele.
This number is very similar to the original frequencies of alleles within that given
Therefore, it would take 1000 generations for the allele frequency for A to
change from 0.9 to 0.81.
Mutation can cause substantial change in allele frequencies but it does slowly.
See Page 211 for clarification and the math shown
Mutation and Selection
It is not correct to assume that mutation is unimportant because of its unappreciable changes in
the allele frequencies of a population
Mutation combine with selection can become a crucial piece of the evolutionary process.
o Read experiment on page 212 and 213.
o The experiment shows that while mutation itself is only a weak mechanism of evolution,
it nonetheless supplies the raw material on which natural selection acts.
o Mutation is the ultimate source of genetic variation.
Most mutations are deleterious.
Selection acts to eliminate such mutations from populations.
Deleterious alleles persist, however, because they are continually created anew.
When the rate at which copies of a deleterious alleles are being eliminated by selection is
exactly equal to the rate at which new copies are beings created by mutation, the frequency of
the allele is at equilibrium mutation-selection balance.
What is the frequency of the deleterious allele at equilibrium?
o ^q = √(µ/s) *The ^ should be on top of the q.
o µ is the mutation rate and s is the selection coefficient (between 0 and 1) which