Name ____________________
AP Biology
Hardy-Weinberg Law Questions
The Hardy-Weinberg Law expressed as p2 + 2pq + q2 =1, allows the calculation of allele
and genotype frequencies in a population. In this investigation, you will determine allele
and genotype frequencies for a single human trait.
Tongue rolling is controlled by a single gene. Persons homozygous dominant or
heterozygous can roll their tongue. Homozygous recessive individuals cannot.
Previous students in AP Biology performed an investigation on tongue rolling. Data from
2010-2012 are compiled in the data table below. Use this information to determine
phenotype numbers for the tongue rolling trait.
Phenotypes
Number of
rollers
Number of
non-rollers
48
7
Fraction with homozygous recessive genotype (q2)
Frequency of recessive allele (q)
Frequency of dominant allele (p= 1-q)
Fraction with homozygous dominant genotype (p2)
Fraction with heterozygous genotype (2pq)
2. From the data, calculate q2, the fraction of individuals who are homozygous recessive
for the trait (those that cannot roll their tongue). Express this as a decimal value in the
appropriate location in the data table above.
3. Calculate q, the frequency of the recessive allele & record the answer in the data table.
4. Determine the frequency of the dominant allele, p, by using the formula p= 1-q.
Record your answer in the data table.
5. Calculate & record the frequencies of the homozygous (p2) dominant and heterozygous
(2pq) genotypes.
Analysis & conclusions
1. What are the frequencies for the alleles that affect tongue rolling?
2. Is q, the frequency of the recessive allele, larger or smaller than the frequency of
people showing the recessive trait? Explain.
3. If you tested 10,000 people, do you think the genotype frequencies would be the
same as those in your class? Explain.
4. If all Hardy-Weinberg conditions were met, what would be the next generation’s
allele frequencies?
5. In a population, 64% of individuals show the recessive trait.
a. What % of the population is pure dominant?
b. What % of the gene pool is recessive?
c. What % of the population is hybrid?
6. If 20% of the gene pool is recessive, what % of the population would be
a. Homozygous dominant?
b. Recessive?
c. Hybrid?
7. A plant population consists of 84% of plants with red flowers and 16% with white
flowers. Assume the allele for red (R) is dominant and the white allele (r) is
recessive.
a. Determine the value of p.
b. Determine the value of q.
c. Solve p2 + 2pq+q2= 1
8. A population consists of 9% white sheep and 91% black sheep. What is the
frequency of the black-wool allele if black is dominant and white is recessive?
9. After test-cross experiments, it was determined that the frequencies of
homozygous dominant, heterozygous, and homozygous recessive individuals for a
particular trait were 32%, 64%, and 4% respectively.
a. What are the dominant (p) and recessive (q) allele frequencies?
b. Is this population in true Hardy-Weinberg equilibrium? If not what type of
selection is occurring?
10. Suppose a population of organisms with 650 gene loci is fixed at half of these
loci, and has 2 alleles for each of the other loci. How many alleles are found in its
gene pool? Explain.
11. In an insect population, a gene can have one of two slightly different sequences
designated A1 and A2. 80% of the gametes produced have the A1 sequence. If the
population is in Hardy-Weinberg equilibrium, what proportion of the insects have
both A1 and A2?
12. At a locus with a dominant and a recessive allele in Hardy-Weinberg equilibrium,
36% of the individuals are homozygous for the recessive allele.
a. What is the frequency of the dominant allele in the population?
b. What percentage of the population shows the dominant trait?