Both members of a human couple know that they are carriers of
the galactosemia allele, a recessive metabolic disorder. None of
their three children have the disease, but any of them may be a
carrier. The couple would like to have a fourth child, but they are
worried that the child would very likely have the disease, since
the first three do not. If the couple came to you with their
worries, what would you tell them?
Would it remove any of the uncertainty in their prediction if
they could find out from genetic tests whether their first three
children are carriers of the disease? Why or why not?