What are the chances of two CFTR gene carriers having a child with two normal alleles?

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An individual with CF is a homozygote, or an individual possessing two abnormal CFTR alleles. Each parent of a child with CF is an obligate carrier (or heterozygote), possessing one normal CFTR allele and one mutated allele. Each child of two carriers has a 1 in 4 chance of having CF, a 2 in 4 chance of being a carrier, and a 1 in 4 chance of having two normal alleles.

What Are the Chances of Two CFTR Gene Carriers Having