Practice problems for exam 2
1.
In a population of 800 people, 32 individuals suffer from a recessive inherited disorder.
Calculate the frequencies of the “disease” and “normal” alleles. Using the allele frequencies you
calculated above, calculate how many individuals you would expect to be homozygous for the
“normal” allele and how many individuals you would expect to be heterozygous for the
“normal” and “disease” alleles.
2. In humans the COL1A1 locus codes for a certain collagen protein found in bone. The normal
allele at this locus is denoted with S. A recessive allele s is associated with reduced mineral
density and increased risk of fractures in both Ss and ss women. A recent study of 1,778 women
showed that 1,194 were SS, 526 were Ss and 58 were ss. Showing your calculations, determine
whether these two alleles are in Hardy-Weinberg equilibrium in this population.
3. On a remote archipelago in the Pacific Ocean lives a population of large flightless pigeons that
occurs on several islands in the archipelago. You visit the first island in the chain and are able to
take blood samples from the pigeons. From your analysis of these samples you determine the
genotypes of all the birds for a particular gene. In the population there are 200 birds with the
following genotypes:
88 AA
64 Aa
48 aa
Showing your calculations demonstrate that this population is not in Hardy Weinberg equilibrium. You
will need to figure out the allele frequencies from the data above and then use the Hardy-Weinberg
formula.
4. On a remote island in the South Atlantic Ocean lives a population of red-eared squirrels. You
visit the island and find the population has 400 adults with the following genotypes:
144 AA
192 Aa
64 aa
Showing your calculations, tell me whether or not this population is in Hardy Weinberg equilibrium. You
will need to figure out the allele frequencies from the data above and then use the Hardy-Weinberg
formula. Show your calculations.
The next year you return to the island to examine the offspring of the previous year’s red-eared squirrels
(young red-eared squirrels don’t have red ears so you can easily identify them). You discover the
following genotypes among the 200 offspring you examine.
68 AA
105 Aa
27 aa
Using your allele frequency data from the previous generation show that this generation (the offspring
generation) is not in Hardy-Weinberg equilibrium Show your calculations.
5. Two alleles A1 and A2 are the only alleles present in a gene pool. The frequency of A1 is 0.9 and
the frequency of A2 is 0.1. The fitnesses of the different genotypes are w11 = 0.8, w12 = 0.8, w22 =
2.0, where w11 is the fitness of the A1A1 genotype, etc.]. Calculate the frequency of the A1 allele
after one generation of selection. What percentage change in the allele frequency of A1 Is this?
Using the same fitness values, if the starting frequency of A1 was 0.6 and A2 was 0.4 what would the
frequency of the A1 allele be after one generation of selection? What percentage change in the allele
frequency of A1 is this? Is there a difference from what you found in the first situation? If so, explain
why that might be?