PKU is a recessively inherited disease. Two

parents who have never been diagnosed with the

disorder have a baby that tests positive for PKU.

Which of the following is the best explanation?

Answer

If PKU is a recessively inherited disease, and the baby got it without either parent having it, then you can use a pedigree to figure out what kind of disease it is (whether autosomal or sex-linked). You can automatically cancel out sex-linked because we don't know the gender of the baby, so you can conclude that PKU is autosomal recessive in this family.

Does that make sense?