BIO 112, Fall 2007 Dr. Paradise
EVOLUTIONARY MECHANISMS PROBLEM SET
Work the following problems before you arrive at lab on 9/5 or 9/6. The first four refer to
the population of mice in the computer simulations; some of the rest may challenge you further.
1. Assume that the frequency of the black allele in the population is 0.6, and that the
population meets all of the expectations of the Hardy-Weinberg equilibrium theory. What are
the expected genotype frequencies for the coat color locus in this population? Show your
work.
Here, the black allele is A, whose frequency is denoted by p. p = 0.6 and q = 0.4.
p
2
thus = 0.36, 2pq = 0.48, and q
2
= 0.16
2. If the population continues to meet the assumptions of the Hardy- Weinberg Equilibrium
theory, do you expect the allele and genotype frequencies at this locus to change drastically
over time? Explain your answer.
Assuming that observed initial frequencies equaled expected frequencies, then the
allele and genotype frequencies should not change over time.
3. Now investigate the coat color locus in another large population of this mouse species. In a
sample of 100 mice from this population you find 60 with black coats, 10 with gray coats,
and 30 with white coats. Calculate the allele and genotype frequencies in this sample.
Allele frequencies are 0.65 (p = [(# of black mice *2)+(# of gray mice)]/2*number of
mice), and 0.35 (q). Genotype frequencies are p
2
= 0.42, 2pq = 0.46, and q
2
= 0.12.
4. Is there evidence to suggest that evolutionary mechanisms are operating on the coat color
locus in this population? (This will require you to compare your observed genotype
frequencies with those predicted by Hardy Weinberg - show your work) If so, which
evolutionary mechanisms would most likely cause such deviations from Hardy-Weinberg
expectations?
There are far fewer heterozygotes than predicted by H-W Theory. This suggests a
couple of possible mechanisms. Positive assortative mating, selection against gray
mice, selection for black and white mice, or emigration of gray mice out of the
population are all possibilities. Can you think of others? Can you devise an
experiment or study to test which mechanism is in action?
5. In the plant Phlox the alcohol dehydrogenase (ADH) locus shows two alleles a and b. The
following genotypic frequencies were found in a population; aa = 0.05, ab = 0.35, bb = 0.60.
Calculate the allele frequencies.
Frequency of the “a” allele is 0.225 and frequency of the “b” allele is 0.775.
6. In a sample of minnows from a local stream, three genotypes controlled by 2 alleles (a
1
& a
2
)
at one esterase locus showed the following numbers in the population; a
1
a
1
= 10, a
1
a
2
= 75,
and a
2
a
2
= 15. Are these numbers what you would expect if this population were in Hardy-
Weinberg equilibrium? If not, is one microevolutionary mechanism more likely to be acting
