A prospective groom, who is not affected by cystic fibrosis (CF), has a sister with cystic fibrosis, an autosomal recessive disease. Their parents are also not affected. The brother plans to marry a woman who has no history of CF in her family. What is the probability that they will have a child with CF? They are both Caucasian and the overall frequency of CF in the Caucasian population is 1/2500 - that is, 1 affected child per 2500 (assume the population meets the Hardy-Weinberg assumptions).