Name: ______________________________
ID: ______________________________
TAKE HOME EXAM I - ECOLOGICAL GENETICS
BIOL 5240 – SPRING 2005
DUE ON TUESDAY MARCH 1
3. Below is data from two towns in Africa where malaria is a health problem. The stronger
economy of the city attracts people from the nearby village who move there to seek employment.
Calculate: 1) the relative fitness, and 2) the selection coefficient for each genotype in the city
population and in the nearby village.
NUMBER OF
GENOTYPE
PEOPLE WITH
THAT
GENOTYPE
ABSOLUTE
FITNESS OF THE
GENOTYPE
RELATIVE
SELECTION
FITNESS
COEFFICIENT
City population
AA
AS
SS
AC
SC
CC
1000
2000
998
0
2
0
4.5
5.0
0.9
4
3.5
6.5
Nearby village
AA
AS
SS
AC
SC
CC
10
35
15
5
3
7
4
6
0.5
4
3.5
7
A. Calculate the relative fitness of the city population and village population.
B. Using the concept of Wright’s shifting balance theory, describe the process by which the
advantageous C allele might spread into the city population sometime in the future.
4. Okapi is an elusive species of forest giraffe that lives in central Africa. This
species is so quiet and well-camouflaged that it is rarely seen. Okapi was one of
the last large mammals to be described by western science. The species was
identified and named in 1915 based on skins that had been collected by local
villagers. In 1985, a research station was established by the Wildlife
Conservation Society in the Ituri forest of Zaire to study this species.
Researchers used pit traps and radiotelometry to track the movements of individuals between
interior forest populations and forest edge populations that occur near human habitation. The
researchers found that the average size of interior populations was 43 whereas the average size of
populations near the forest edge was only 7. Furthermore, they estimated that about 4
individuals migrated into the interior populations per generation but only 1 migrant entered the
edge populations. Because so few animals fell into their pit traps, they decided to extract DNA
from dung samples to assess the extent of population divergence. In 2001, the research station
was shut down and all foreign scientists were evacuated due to political instability in the region.
Below are microsatellite gels that show the genotypes of 10 individuals sampled from one
interior and one edge population.
Interior Population
Edge Population
Individuals sampled
Individuals sampled
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
A. Do the genotypic frequencies of either of these two populations deviate from Hardy-Weinberg
expectations?
B. Assuming an island model of gene flow, calculate allele frequencies for each population after
five generations.
C. According to your calculations, what effect is migration having on genetic diversity in each of
these populations?
D. Does the extent of inbreeding differ between the interior population and exterior population
based on the microsatellite data?
E. Calculate the statistic that indicates the extent to which these populations are genetically
diverged? Does this value represent a lot of divergence, moderate divergence, or little
divergence?
F. What is going on in these populations?
ANSWER 3 OF THE FOLLOWING 5 QUESTIONS
5. In lecture, I repeatedly emphasized the point that when an allele is rare, it occurs more often
in heterozygotes rather than homozygotes (assuming HW). Explain two instances when this
strongly influences the efficacy of selection.
6. What if you did a study and found no relationship between genetic variation at microsattelite
loci and fitness? Would you be surprised? Why or why not?
7. Why is the “effective population size” different from actual number of individuals in a
population in many cases?
8. Molecular biology has revealed an astonishing amount of genetic variation in organisms.
However, there are very few cases where we can take our knowledge about variability in any
particular gene and understand how it impacts the fitness of real organisms in nature. Why?
9. Distinguish between positive and negative frequency-dependent selection. Which one is more
commonly found in nature? Why do you think that is true?