Q. In humans, nearsightedness and phenylketonuria are both inherited as single-locus autosomal recessive traits that assort independently. Imagine that a family has been identified in which both parents were phenotypically normal, other than their first child was phenylketonuric and their second child developed nearsightedness.

a. What is the possibility that their next child will show both defects? Demonstrate the work.

b. What is the probability that their next child will exhibit neither defect? Explain the work.