Hardy-Weinberg Problems
Name __________________________________
Albinism
Albinism is a rare genetically inherited trait that is only expressed in the phenotype of homozygous recessive
individuals (aa). The most characteristic symptom is a marked deficiency in the skin and hair pigment
melanin. This condition can occur among any human group as well as among other animal species. The
average human frequency of albinism in North America is only about 1 in 20,000.
The Hardy-Weinberg equation is: ________________________.
In this equation, the term that is equal to the frequency of homozygous recessive individuals (aa, in this case)
in a population is ____. Therefore, given the information provided above, the frequency of homozygous
recessive individuals (expressed as a decimal) will be: q² = ____________, or if multiplied by 100 to get a
percentage, about _______% of the population. By taking the square root of both sides of this equation (q² and
the value for the frequency), we get the frequency of the recessive albinism allele q = ____________.
If you know one of the two variables (q) in the Hardy-Weinberg equation, it is easy to solve for the other (p).
p= 1–q
p=
p=
The frequency of the dominant, normal allele (A) is, therefore, _____________or about ____ in______.
The next step is to plug the frequencies of p and q into the three terms of the Hardy-Weinberg equation:
p² + 2pq + q² = 1
This gives us the frequencies for each of the three genotypes for this trait in the population:
p² =
predicted frequency
of homozygous
dominant individuals
=
2pq =
predicted frequency
of heterozygous
individuals
=
q² =
predicted frequency
of homozygous
recessive individuals
(the albinos)
=
What does this tell you about the number of people who CARRY the albinism allele, compared to the number of
people who show the trait? Why would we care about alleles that are not actually expressed (expressed=show
up as an observable trait)?
Hardy-Weinberg Problems
Name __________________________________
Flowers in the Mountains
Scenario: Scientists are studying a population of flowers found in a mountain valley. These flowers, called
mountain daisies, come in two colors: yellow and red. There is a different allele for each trait, and the red allele
is dominant over the yellow allele. There are two pollinators (organisms that spread the pollen of flowers,
allowing them to reproduce) found in this valley. The first, the bumblebee, is found in large numbers, and is
attracted primarily to yellow flowers. The second, a hawk moth, is attracted primarily to red flowers. However,
the hawk moth population is very small, since they are sensitive to the cooler temperatures at high altitudes. The
scientists studying the flowers want to determine if climate change will have an affect on the flower population.
They conduct a survey to determine how many flowers of each color are found in the valley population.
1. At the beginning of the study, they determine that 3 out of every 10 flowers are yellow. Based on this data,
calculate:
a. The frequency of homozygous recessive individuals in the population.
b. The frequency of the yellow allele (r) in the population.
c. The frequency of the red allele (R) in the population.
d. The frequency of homozygous dominant and heterozygous individuals in the population
2. Ten years later, the scientists return to the valley. Again, they survey the plants, are surprised to find that
only 1 out of every 30 flowers is yellow. Based on this data, calculate:
a. The frequency of homozygous recessive individuals in the population.
b. The frequency of the yellow allele (r) in the population.
c. The frequency of the red allele (R) in the population.
d. The frequency of homozygous dominant and heterozygous individuals in the population
Hardy-Weinberg Problems
Name __________________________________
3. What explains the large percentage of heterozygous red flowers at the beginning of the study?
4. Based on your calculations, has this population evolved? What evidence do you have? If the population did
evolve, what a possible cause of that evolution?
5. If the climate continues to warm, what do you predict will happen to the allele frequencies in this population?