Final answer:
For an autosomal recessive condition, if both parents are carriers, each child has a 50% chance of being a carrier but unaffected. The correct answer to the student's question is option 3) 50%.
Step-by-step explanation:
When considering the chances that a child will be a carrier of a genetic disorder, we must understand the principles of genetics and inheritance patterns. For autosomal recessive conditions like cystic fibrosis, carrier parents have one normal allele and one recessive allele for the disease (represented as Ff). A child can therefore inherit the following combinations: FF (normal), Ff (carrier), or ff (affected by the disease).
According to a Punnett square analysis for two carrier parents of an autosomal recessive condition, each child has a 25% chance of being unaffected and not a carrier (FF), a 50% chance of being a carrier but unaffected (Ff), and a 25% chance of being affected (ff). For X-linked recessive disorders, the situation is slightly different: a son of a carrier mother has a 50% chance of being affected, while a daughter has a 50% chance of being a carrier.
Therefore, the correct answer to the question, "What are the chances that a child will be a carrier?" is option 3) 50%, assuming that both parents are carriers of an autosomal recessive gene.