AP Biology
Hardy-Weinberg Practice Problems โ ANSWER KEY
1. You have sampled a population in which you know that the percentage of the homozygous recessive genotype
(aa) is 36%. Using that 36%, calculate the following:
A. The frequency of the "aa" genotype (q2). q2 = 0.36 or 36%
B. The frequency of the "a" allele (q). q = 0.6 or 60 %
C. The frequency of the "A" allele (p). p = 0.4 or 40%
D. The frequencies of the genotypes "AA" (p2) and "Aa" (2pq) p2 = AA = 0.16 or 16% 2pq = Aa = .48 or 48%
2. Sickle-cell anemia is an interesting genetic disease. Normal homozygous individuals (HbHb) have normal blood
cells that are easily infected with the malaria parasite. Thus, many of these individuals become very ill from
the parasite and many die. Individuals homozygous for the sickle-cell trait (HSHS) have red blood cells that
readily collapse when deoxygenated. Although malaria cannot grow in these red blood cells, individuals often
die because of the genetic defect. However, individuals with the heterozygous condition (HBHS) have some
sickling of red blood cells, but generally not enough to cause mortality. In addition, malaria cannot survive well
within these "partially defective" red blood cells. Thus, heterozygotes tend to survive better than either of the
homozygous conditions. If 9% of an African population is born with a severe form of sickle-cell anemia (HSHS),
what percentage of the population will be more resistant to malaria because they are heterozygous (HBHS) for
the sickle-cell gene? HBHS = 2pq = 0.42 or 42%
3. There are 100 students in a class. Ninety-six did well in the course whereas four blew it totally and received a
grade of F. Sorry. In the highly unlikely event that these traits are genetic rather than environmental, if these
traits involve dominant and recessive alleles, and if the four (4%) represent the frequency of the homozygous
recessive condition, please calculate the following:
A. The frequency of the recessive allele (q). q = 0.2 or 20%
B. The frequency of the dominant allele (p). p = 0.8 or 80%
C. The frequency of heterozygous individuals (2pq). 2pq = 0.32 or 32%
4. Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all
butterflies are white. Given this simple information, which is something that is very likely to be on an exam,
calculate the following:
A. The percentage of butterflies in the population that is heterozygous. 2pq = 0.47 or 47%
B. The frequency of homozygous dominant individuals. p2 = 0.137 or 13.7%
5. A rather large population of Biology teachers has 396 individuals with poor vision and 557 with good vision
individuals. Assume that poor vision is totally recessive. Please calculate the following:
A. The allele frequencies of each allele. p = 0.35 or 35% q = 0.65 or 65%
B. The expected genotype frequencies. p2 = 0.12 or 12% 2pq = .46 or 46% q2 = 0.42 or 42%
C. The number of heterozygous individuals that you would predict to be in this population. 0.46(953) = 438
D. Conditions happen to be really good this year for breeding and next year there are 1,245 young
"potential" Biology instructors. Assuming that all of the Hardy-Weinberg conditions are met, how many of
these would you expect to have poor vision and how many with good vision? 0.58(1245) = 722 good
vision and 0.42(1245) = 523 poor vision
6. A very large population of randomly-mating laboratory mice contains 35% white mice. White coloring is
caused by the recessive genotype, "aa". Calculate allelic and genotypic frequencies for this population.
q = 0.592 or 59.2% frequency of โaโ allele
p = 0.408 or 40.8% frequency of โAโ allele
p2 = AA = 0.166 or 16.6%
2pq = Aa = 0.483 or 48.3%
q2 = aa = 0.35 or 35%
