Question

A) 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?

b) 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?

Answer 1

If both parents are carriers, there is a 25% chance the child will have the disease. If only one parent is a carrier, there is a 0% chance the child will have the disease but a 50% chance the child will be a carrier.

Step-by-step explanation:

In this case, the couple are carriers of the galactosemia allele, which is a recessive metabolic disorder. None of their three children have the disease, but they could be carriers. The probability of their fourth child having the disease depends on whether both parents are carriers or if only one parent is a carrier. If both parents are carriers, there is a 25% chance the child will have the disease. If only one parent is a carrier, there is a 0% chance the child will have the disease but a 50% chance the child will be a carrier. It's important to note that genetic testing of the first three children would not remove the uncertainty in predicting if the fourth child will have the disease because the outcome depends on the genetic makeup of the parents.