1. Is the CFTR allele maintained by mutation/selection balance?
In some populations: Fraction infected with Cystic Fibrosis: 2%
Under mutation/selection balance (eq. Freq. of q = m / s), need:
m = 4 x 10-4
However the actual (estimated) rate is 6.7 x 10-7
too low!

2. Cultured mouse cells with CFTR genotypes
The fitness cost
of dF508 / dF508
with respect to
Pseudomonas
is balanced by the
fitness advantage
of dF508 / +
Salmonella

3. Migration can alter allele and genotype frequencies. Migration is a
Incorporating Migration
Migration can alter
allele and genotype
frequencies.
Island
Geneflow
Migration is a
homogenizing
force; it prevents
divergence of
populations
Continent

4. Lake Erie
Water Snakes
Banded vs Unbanded

5. Natural Selection for Unbanded Forms on Islands

6. It is possible to calculate the change in frequency
Incorporating Migration
Banded alleles
Island
It is possible to calculate
the change in frequency
of the banded allele (q)
as a function of q.
Opposed by
Natural Selection
Continent

7. Change in frequency of the unbanded allele (q) as a function of q.
Equilibrium points

8. In populations of finite size, sampling of gametes
Incorporating Genetic Drift
In populations of finite size, sampling of gametes
from the gene pool can cause evolution

9. If 10 zygotes are sampled
from a population with
p = 0.6, q = 0.4.

10. Probability of Maintaining the
Same Initial Allele Frequency

11. The Ultimate Fate of Genetic Drift:
Random Fixation or Loss of Alleles

12. The Effects of Drift are More Pronounced in Smaller Populations

13. 8 pops
The frequency
of heterozygotes
decreases under
drift.
Hg+1 = Hg[1-1/2N]

14. Effective population size
Ne = 4NmNf / (Nm + Nf)
Effective population size

15. Rate of Evolution by Genetic Drift
equals rate that
an allele is fixed
at a locus.
Depends upon: (2Nu) number of mutations arising at locus
per generation, and initial frequency of new allele (1/2N)
K = 2Nm x 1/2N = m
rate of allele substitution = rate of mutation!

16. Neutralist view: allele substitution and polymorphism
are determined by the same evolutionary process.
Mutation provides a continual supply of new alleles.
Because many alleles are neutral
or effectively neutral, alleles
becomes fixed or lost from a
population as a result of
genetic drift.
Polymorphism is simply a snapshot of a continuous
process of mutational input and subsequent random
extinction or fixation of alleles.

17. Mootoo Kimura’s concept of neutralism is illustrated in the following diagram from his original paper.

18. Selectionist view: allele substitution and polymorphism
are determined by different, selective processes.
Mutation yields advantageous
alleles that are driven to fixation by
positive natural selection.
Two or more alleles are maintained
at a locus in a population by
over dominance.