Hardy Weinberg Study Questions
These questions are designed to sharpen your understanding of the Hardy-Weinberg
equilibrium and related
concepts..
1. If the frequency of a homozygous dominant genotype in a randomly mating population
if 0.09, what is the
frequency of the dominant allele? What is the combined frequency of all other alleles of
this gene that may be
present in this population? Answer
2. Which of the following genotype frequencies of AA, Aa and aa, respectively, satisfy the
Hardy Weinberg
equilibrium: Answer
a. .25 .5 . 25
b. .36 .55 .09
c. .49 .42 .09
d. .64 .27 .09
e. ,29 .42 .29
3. Hartrup disease is an recessive disorder of intestinal transport of amino acids. Its
frequency in newborns is
about 1 in 14,000. Assuming random mating, what is the frequency of heterozygotes? Answer
4. A randomly mating population of dairy cattle contains a recessive allele causing
dwarfism. The frequency of
dwarf calves is 10%. What is the frequency of heterozygous carriers of the allele in the
entire herd? What is the
frequency of heterozygotes among the non-dwarf cattle? Answer
5. In certain grasses, the ability to grow in soil contaminated by the toxic metal nickel
is determined by a dominant allele for resistance. Answer
a. If 60% of the seeds in a randomly mating popualtion are able to grow on contaminated soil, what is the frequency of the resistance allele?
b. Among the plants that germinate, what proportion are homozygous?
6. Three different genotypes were observed among 35 individuals in a randomly breeding
natural population.
The numbers of each genotype in the sample were as follows: Answer
AA 2 Aa 13 aa 20
What is the frequency of each of the two alleles in the population. If the population
consisted of 350 individuals
and was at Hardy Weinberg equilibrium, what numbers of each genotype would you predict?
7. The Hardy Weinberg equilibrium can be extended to gene loci with 3 alleles in a natural
population (though
every diploid individual can have only two of these) by considering the relationship p + q
+ r = 1, where p, q,
and r are the gametic frequencies. Write an expression for all zygotic (genotypic)
frequencies in this case
(hint: remember that for the 2 allele case, the HW formula can be written as (p + q)2
----don’t forget to include
all the different heterozygous genotypes). Answer
8. (This question is a bit more challenging. Be sure to write down all the genotypes that
can result in a particular
phenotype; e.g., type “A” can be IA I0 as well as IA IA.) In a Pygmy group in
Central Africa, the frequencies
of some of the alleles determining the ABO blood groups were determined to be roughly as
follows: Answer
IA .74 IB .10
a. What is the frequency of the third allele (I0)?
b. Assuming random mating, what are the frequencies you would expect of all 4 ABO bloodtypes (A, B, AB and O) in this group.
9. (This questions requires a little bit of calculus). We can define the heterozygosity
of a population “H” as the
frequency of heterozygotes, or, for the two allele case, 2pq. For what value of p is
heterozygosity at a maximum? What about the 3 allele case? Answer
Credits: Ques. 1 - 6 and 8 are from D.L. Hartl, Genetics, 3rd Ed. Jones & Bartlett,
Boston, London.
1994 with slight modifications.