Answer to Hardy-Weinberg Quiz

One out of 10,000 babies is born with PKU, a metabolic disease that causes mental retardation and other
problems. The disease is caused by a recessive allele.


What is the frequency of the genotype of the individuals in the population born with PKU?

What is the frequency of the recessive allele?

What is the frequency of the dominant allele?

What is the frequency of the carriers in the population.

What percentage of the population are carriers of the PKU allele?


Answer: One out of 10,000 babies is born with PKU, a metabolic disease that causes mental retardation and
other problems. The disease is caused by a recessive allele, and thus the frequency of the individuals in the
population born with PKU corresponds to q2 in the Hardy-Weinberg equation. Given one PKU occurrence per 10,000 births, q2=0.0001. The frequency of the recessive allele is 0.01 or 1%. Therefore, the frequency of the dominant allele is p=1-q or 0.99. The frequency of the carriers in the population is equal to 2pq or 2(.99)(0.01) =0.0198 or 1.98%. That means that about 2% of the population is carriers of the PKU allele.

Adopted from BiologyForLife