1. XPA is a recessive DNA repair disorder that causes skin cancer with even the smallest exposure to sunlight. Heterozygotes (Xx) are carriers, but are not affected. In the U.S., 1/250,000 people have the disease. In Japan, 1 in 22,000 has the disease. What is the frequency of the mutated XPA allele (x) in each population?

2. Phenylthiocarbamide (PTC) tastes bitter to most people. The inability to taste PTC is controlled by a single recessive allele. In the Australian Aboriginal population, 58% can taste PTC, and 42% cannot. Estimate the allele and genotype frequencies of the taster (T) and non-taster (t) allele in this population.

3. Sickle-cell anemia is caused by receiving two copies of a recessive allele on Chromosome 18Q. The recessive allele has a deletion mutation that causes problems with the hemoglobin complex, and red blood cells curl into a sickle shape as a result. One in 500 African Americans has sickle cell anemia. One in 36,000 Hispanic Americans has the disease.

What is the frequency of the sickle cell allele in these two populations?

What percentage of these two populations will be carriers of the trait, but not have the disease?