AP Biology— Hardy-Weinberg Problem Set ANSWER KEY
p2 + 2pq + q2 = 1
Name_______________________
p+q=1
p = frequency of the dominant allele in the population
q = frequency of the recessive allele in the population
p2 = percentage of homozygous dominant individuals
q2 = percentage of homozygous recessive individuals
2pq = percentage of heterozygous individuals
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. 0.36
B. The frequency of the "a" allele. 0.6
C. The frequency of the "A" allele. 0.4
D. The frequencies of the genotypes "AA" and "Aa." AA=0.16
Aa=0.48
E. The frequencies of the two possible phenotypes if "A" is completely dominant over "a." Dominant = 0.64
Recessive = 0.36
2. The allele for a hitchhiker's thumb is recessive compared to straight thumbs, which are dominant. . In a
population of 1000 individuals, 510 show the dominant phenotype. How many individuals would you expect for
each of the three possible genotypes for this trait? AA = 90 Aa = 420 aa = 490
3. Sickle-cell anemia is an interesting genetic disease. Normal homozygous individuals (SS) have normal blood cells
that are easily infected with the malarial parasite. Thus, many of these individuals become very ill from the
parasite and many die. Individuals homozygous for the sickle-cell trait (ss) 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 (Ss) 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 (ss), what percentage of the population will be
more resistant to malaria because they are heterozygous (Ss) for the sickle-cell gene? Ss = 42%
4. 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. 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 = 0.2
B. The frequency of the dominant allele. p = 0.8
C. The frequency of heterozygous individuals. 2pq = 0.32
5. The allele for a widow's peak (hairline) is dominant over the allele for a straight hairline. In a population of 500
indiviuals, 25% show the recessive phenotype. How many individuals would you expect to be homozyous dominant
and heterozygous for the trait? AA = 125 Aa = 250
6. 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, calculate the following:
A. The percentage of butterflies in the population that are heterozygous. Bb = 47%
B. The frequency of homozygous dominant individuals. BB = 13%
7. Cystic fibrosis is a recessive condition that affects about 1 in 2,500 babies in the Caucasian population of the
United States. Please calculate the following.
The frequency of the recessive allele in the population. _0.02_
The frequency of the dominant allele in the population. _0.98_
The percentage of heterozygous individuals (carriers) in the population. _3.92%_
8. Below is a data set on wing coloration in the scarlet tiger moth (Panaxia dominula). Coloration in this species
had been shown to behave as a single-locus, two-allele system with incomplete dominance. Data for 1612
individuals are given below:
White-spotted (AA) =1469
Intermediate (Aa) = 138
Little spotting (aa) =5
Calculate the allele frequencies ( p and q ) p = 0.944 q = 0.056
9. A very large population of randomly-mating laboratory mice contains 35% white mice. White coloring is caused
by the double recessive genotype, "aa". Calculate allelic and genotypic frequencies for this population.
q2 = 0.35 q = 0.59 p = 0.41 p2 = 0.17 2pq = 0.48
10. The ability to taste PTC is due to a single dominant allele "T". You sampled 215 individuals in biology, and
determined that 150 could detect the bitter taste of PTC and 65 could not. Calculate all of the potential
frequencies. q2 = 0.30 q = 0.55 p = 0.45 p2 = 0.20 2pq = 0.50
11. A large population of laboratory animals has been allowed to breed randomly for a number of generations.
After several generations, 43% of the animals display a recessive (aa) phenotype. The rest of the animals show the
dominant phenotype, with heterozygotes indistinguishable from homozygotes.
A. What is the estimated frequency of the ‘a’ allele? q = 0.66
B. What proportion of the population is probably heterozygous (Aa) for this trait? 2pq = 0.45
12. In peas, a gene controls the flower color such that R = red and r = white. In an isolated pea patch, there were
22 red flowers and 78 white flowers. What is the value of q for this population? What is the value of p for this
population? q = 0.88 p = 0.12