1. Briefly describe the endosymbiont hypothesis. Describe one piece of evidence supporting the
hypothesis. 5 points
2. There are two alleles, B and b, at a gene in a population. You determine the number of
individuals having genotypes, BB, Bb, or bb. The observed numbers are BB (n=27), Bb (n= 52),
bb (n = 108). What are the allele frequencies of B and b in this sample of individuals? Show
work. 5 points
3a. The smooth pea vs. wrinkled pea phenotype is due to two alleles (R and r) at the R locus.
The smooth allele, R, is dominant. In a cross between Rr and rr parents, what proportion of
resulting offspring is expected to be wrinked? Explain how you got your answer (NO PUNNETT
SQUARES ALLOWED!), using sentences and/or diagrams. 5 points
b. If you carried our this cross, do you think the observed proportion of wrinkled vs. smooth
offspring would be closer to the expected proportion if you had a large number or a small
number of offspring? Explain. 3 points
4. Figures A and B show the relationship between the heights of identical and fraternal twins.
One twin’s height is marked along the x-axis, and his or her twin sibling’s height is marked on
a. In part A, can you predict the height of Twin 2 when twins are identical? For example,
what would you expect the height of Twin 2 to be if the height of Twin 1 is 160 cm? 2
b. In part B, can you accurately predict the height of Twin 2 if fraternal Twin 1 is 160cm?
What range of heights might be observed for Twin 2? 2 points
c. What might be contributing to the height variation for fraternal twins? 2 points
5. Explain why information on both the heritability of a trait and the strength of selection on a
trait are needed to predict how fast a trait will evolve if acted upon by directional selection. 6
6a. Explain the difference between the neutral mutation rate and the mutation rate. 3 points
b. How does the concept of “functional constraint” relate to the concept of the neutral mutation
rate? 3 points
7. In large populations, what is the difference in the timescales of the spread of beneficial vs.
neutral mutations? 5 points
8. The histogram below shows data comparing rates of sequence evolution in mammals for
different classes of DNA sequences. Assume the variation is explained by the neutral theory.
a. What are pseudogenes? 3 points
b. Under the neutral theory, what is the most likely biological interpretation of the observation
that 5’-untranslated regions (UTRs) evolves more slowly than pseudogenes? 3 points.
c. which sequence class is most functionally constrained? 2 points