Chapter 20, Problem 26P

In Europe, the frequency of the CF allele causing the recessive autosomal disease cystic fibrosis is about 0.04. Cystic fibrosis causes death before reproduction in virtually all cases.

a.	Determine values of relative fitness (W) for the unaffected, carrier, and affected genotypes. Assume that no selective advantage is associated with heterozygosity for the disease allele.
b.	Given your answer to part (a), determine the average (mean) fitness at birth of the population as a whole with respect to the cystic fibrosis trait ( $\stackrel{-}{W}$) and the expected change in allele frequency over one generation (Δq) when measured at the birth of the next generation.
c.	Suppose the European population is at equilibrium for the frequency of the CF- allele because some heterozygote advantage exists. Recalculate the relative fitness values for the three genotypes under this assumption
d.	The CFTR protein encoded by the CF gene is a chloride ion channel. People suffering from cholera have diarrhea that pumps water and chloride ions out of the small intestine. Use these facts to explain why a heterozygote advantage might in fact exist for the CF gene