Cystic fibrosis is an autosomal recessive condition. A couple who are both carriers (heterozygous) for the gene for cystic fibrosis have two children who have cystic fibrosis. N= noncystic fibrosis allele, n= cystic fibrosis allele

a. For this trait, what is the genotype for the two children with cystic fibrosis? Why?

b. What is the probability that their next child will have cystic fibrosis? Why?