Worksheet for Tutorial 34: Genes in Populations
1. In this tutorial, we are shifting from a focus on genetics at the individual level to genetics
at the population level. Based on what you read in tutorial 34, define the terms population
and species in the space below:
Population:
Species:
2. Fill in the blank. Natural selection acts on ___________.
3. Fill in the blank. Evolution acts on ____________.
4. Scientists use the Hardy-Weinberg equation to quantify allele frequencies within a
population. There are two different versions of the Hardy-Weinberg equation that provide
us with different types of information. The equation below tells us about allele
frequencies within a population. The chart below the equation defines the variables used
in the equation.
H-W equation for allele frequency: p + q = 1
Variable
p
Dominant/Recessive
Dominant
q
Recessive
5. There is also a Hardy-Weinberg equation for genotype frequency provided below. The
chart below the equation defines the variables used in the equation.
H-W equation for genotype frequency: p2 + 2pq + q2 = 1
Genotype
Homozygous Dominant
Variable
p2
Heterozygous
2pq
Homozygous Recessive
q2
Now that we have defined the variables for both equations, it is time to apply these equations to
an example.
6. You are a researcher studying a heffalump population in the Hundred Acre Wood. You
know that some heffalumps have hair, while others are hairless. The H allele codes for
hair, and is completely dominant. The h allele is recessive and codes for no hair. Use this
information to fill in the chart below:
Allele
Dominant/Recessive
Variable
H
h
7. Before moving on, fill in the chart below to define the phenotype associated with each
genotype. You should also fill in the variable representing each genotype in the HardyWeinberg equation for genotype frequencies.
Genotype
Phenotype
Variable
HH
Hh
hh
8. You travel through the Hundred Acre Wood and count a total of 100 heffalumps. Out of
the 100 heffalumps you counted, 84 had hair, and 16 had no hair. What is the frequency
of the h allele? Explain how you calculated this frequency.
9. What is the frequency of the H allele? Explain how you calculated this frequency.
10. Now that you know the frequency of each allele in the heffalump population, calculate
the number of heterozygous heffalumps within the Hundred Acre Wood population.
Explain how you calculated your answer.
11. How many homozygous dominant individuals are there in the population? Explain how
you calculated your answer.
12. Can you determine the genotype of a hairy heffalump just by looking at it? Why or why
not?
13. Can you determine the genotype of a hairless heffalump just by looking at it? Why or
why not?
14. List the five factors that can influence changes in allele frequencies, and explain how
each factor can change allele frequencies within a population.