What Is Life? 2nd Edition by Jay Phelan

Exercise 41

Individuals carrying two non-functioning alleles for the gene producing the enzyme that converts phenylalanine into tyrosine:
A) will develop phenylketonuria (PKU).
B) may or may not develop phenylketonuria, because the environment (diet, in this case) also plays a role in determining their phenotype.
C) will develop both PKU and Tay-Sachs disease, because the genes causing the two traits are on the same chromosome.
D) will develop both PKU and Tay-Sachs disease, because one pleiotropic gene influences both traits.
E) do not need to worry about their phenylalanine consumption, because PKU depends on both genes and the environment.