Cystic fibrosis is a homozygous recessive condition. A genetic counselor should advise concerned potential parents that, if they are both carriers, the probability of their child having cystic fibrosis is ________.

Question

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To have cystic fibrosis, a child must inherit one copy of the cystic fibrosis transmembrane conductance regulator (CFTR) gene mutation from each parent. People who have only one copy of a CFTR gene mutation do not have CF. They are called "CF carriers."
A CF carrier is heterozygous for the gene (Cc). In order to determine the potential for a child to have CF, we can draw out a Punnett Square:
 11ec0fb7_2809_69ce_95f0_f30e4102423c_NR0002_00 Each time two CF carriers have a child, the chances are:
25 percent (1 in 4) the child will have CF
50 percent (1 in 2) the child will be a carrier but will not have CF
25 percent (1 in 4) the child will not be a carrier of the gene and will not have CF

Cystic Fibrosis Is a Homozygous Recessive Condition