1. The ability to roll the tongue is controlled by a single gene with two alleles.  The allele for being able to roll is dominant over the allele for not being able to roll.  In a given population of 10,000 individuals there are 7399 tongue rollers and 2601 non-rollers.  Assuming the population is at Hardy-Weinberg equilibrium, how many heterozygous tongue rollers are there in the population?

(p+q)² = p² + 2pq + q² = 1
Let p = allele frequency for rolling
Let q = allele frequency for non-rolling
q² = 2601/10,000 = 0.2601
q = 0.51
p = 1 - q = 0.49
2pq = 2(0.49)0.51 = 0.4998
Number of heterozygous rollers = 0.4998(10,000) = 4998

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2. In a population of 100,000 human babies in a given locality:
    20,460 babies were born with totally sickled red blood cells
    59,290 babies were born with partially sickled red blood cells
    20,250 babies were born with normal red blood cells.
Is the baby population at Hardy-Weinberg equilibrium? NO (see math below)

In what part of the world do you think this population is located (include reasoning)?  An area with malaria, as heterozygouse individuals are more common than in an equilibrium population

What type of selection may this population be undergoing? Stabilizing (extremes selected against)

(p+q)² = p² + 2pq + q² = 1
Let p = allele frequency for HbS
Let q = allele frequency for HbA
q² = 20,460/100,000 = 0.2046
q = 0.4523
p = 1 - q = 0.5477
p²(calculated) = 0.3000   p ²(actual) = 20,250/100,000 = 0.2025
2pq(calculated) = 2(0.49)0.51 = 0.4998  2pq(actual) = 59,290/100,000 = 0.59290

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3. Phenylketonuria (PKU) is a disease in which people who are homozygous for the recessive PKU allele lack the ability to properly breakdown the amino acid phenylalanine.  Build up of phenylalanine and phenylpyruvate, a by-product of incomplete breakdown, cause mental retardation in the children born with PKU.  PKU was one of the first diseases successfully treated by gene therapy.  To anticipate how many individuals will need gene therapy in the next century researchers need to know how prevalent the recessive allele is in the U.S. population.  Given that PKU disease occurs in 1 out of 10,000 births and that the U.S. population is so large that Hardy-Weinberg equilibrium has been achieved for this gene, what is the PKU allele frequency, and how many people carry the allele without suffering from PKU?

The answers are below. On the exam you would have to show all your equations and calculations.
q = 0.0100
2pq = 0.0198 = 1.98% of U.S. population