Phenylketonuria (PKU) is a disease that is caused by the mutation of a single gene. The mutation can cause several problems, such as mental ret*rdation, lightly colored hair and skin, and lower IQ. The disease phenylketonuria is an example of how
A.
a single gene can only affect a single trait.
B.
multiple genes can affect a single trait.
C.
a single gene can affect multiple traits.
D.
all of these