If a genetic disorder were the cause, which answer is most likely correct?

(A) A pollutant is causing mutations.
(B) Multiple alleles are involved.
(C) The disease is caused by a dominant allele.
(D) Baby Pierre's parents are homozygous for a recessive allele causing the disease.
(E) The disease is due to an autosomal recessive.

Explain the reason for your choice.

There is no reason to suspect that answer (A) is correct from the data given. Pollutants are highly unlikely in remote Quebec and they are not likely to casue specific mutations.

The fact that 1/4 of the children are afflicted when the parents aren't suggests a simple 2 allele system involving a defective recessive allele, so answer (B) isn't likely.

Answer (C) can't be correct because if a dominant allele causes the disease, the parents would also show it.

Answer (D) can't be correct because the parents cannot be homozygous for the disease causing recessive; if they were, they too would have the disease.

Answer (E) is the correct choice. The disease clearly is recessive and since females and males were equally afflicted, it is autosomal and not a sex-linked trait.