Question

Sarah and Thomas are thinking about having kids. They are concerned that because Thomas’s father was diagnosed with cystic fibrosis last year, it could run in the family. Cystic fibrosis is a recessive genetic disorder which affects the respiratory system. Both Thomas and Sarah get tested for the recessive allele (f), with the results indicating that they are each carriers of the disorder (a genotype of Ff).
Is it possible for Sarah and Thomas to develop cystic fibrosis?

Answer 1

It is not possible for Sarah and Thomas to develop cystic fibrosis but it would be possible for one of their children to inherit it. Both Sarah and Thomas are heterozygous and in a heterozygous pair of alleles the dominant allele is the one that will present. Because Sarah and Thomas both have the heterozygous allele combination Ff they are carriers which means that they will not experience symptoms of cystic fibrosis but they could pass cystic fibrosis onto one of their children.