BIOL 286 Fall 2021
Homework Assignment 1
Due: Sept 20th
25 points
1. There are three critical components of the theory of evolution by natural selection. Explain what
they are and why all three must be present in order for natural selection to act on a trait (3 points)
2. a. Selection can act on traits in three different ways – stabilizing selection, directional selection,
and disruptive selection. Explain each type and give an example of each (3 points)
b. In a population of frogs, males with a call rate equal to the mean of the population have better
reproductive success than males that call at a different rate. Explain how the distribution shown
in the figure would change in response to this level of selection over generations. Include an
approximation of the new trait distribution curve (you can draw on the same plot or make a new
figure) (2 points)
Call
rate
call rate
3. a. When is sexual reproduction adaptive? (2 points)
b. When is asexual reproduction adaptive? (3 points)
4. a. Define absolute fitness and relative fitness (1 point)
b. Consider a population of crickets in an agricultural field. Secretion of a particular digestive
enzyme in these crickets is determined by two alleles, A and a. The allele frequencies in the
population are A=0.7, a=0.3. If there is no immediate selection on this trait, and Mendelian
inheritance applies, what are the genotype frequencies? What are the number of individuals
with each genotype (Assume population size is 200) (3 points)
BIOL 286 Fall 2021
c. After the field referred to in question (b) is sprayed with a new type of insecticide, the number of
surviving individuals is given below. Calculate the absolute fitness, and relative fitness of each
genotype. Round up the answers to three decimal points. (3 points)
Genotype
Number of individuals survived
AA
70
aa
8
Aa
82
d.
Which genotype has the highest selection coefficient? What does this mean? (1 point)
5
a. You go to Australia and measure the body mass of an entire population of rusty numbats. You then
find that only a subset of these anteaters breed. Given that strength of selection (also called the
selection differential) for body mass in the population = -6, and response to selection = -4, calculate
the heritability of body mass. Show your work. (2 points)
b. Given that the population mean is 14 grams, what will the mass of the average offspring be in the
next generation? (1 point)
c. Is evolution occurring? Why or why not? (1 point)