Marfan syndrome is an autosomal dominant disorder caused by a mutation of the FBN1 gene that affects the connective tissue of the body. Suppose that two parents, a father with genotype FBN1 fbn1 and a mother with genotype fbn1 fbn1, are planning to have a family. What is the probability that they will have an affected daughter as their first child? Enter your answer as a decimal.

The correct answer is 0.25.

Explanation:

An autosomal dominant disorder, resulting due to a mutation of the FBN1 gene is termed as Marfan syndrome. The condition generally affects the body's connective tissues. It is given in the question that the genotype of the father is FBN1fbn1 and the genotype of the mother is fbn1fbn1. The cross between the father and the mother is given below in the attachment,  

Based on the cross, it is clear that 50 percent of the offspring would suffer from the condition or 1/2, and the probability of having a girl child is also 50 percent of 1/2.  

Therefore, the probability of the girl child suffering from the condition would be:  

= 1/2 * 1/2 = 1/4 or 0.25.  

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