Paediatricscommon
A couple attend for genetic counselling. Their 3-year-old son has cystic fibrosis, confirmed by newborn screening and genotyping; both parents are carriers of a *CFTR* mutation. Their 6-year-old daughter is well, has had a normal sweat test and has never had chest or bowel problems. They ask what the chance is that their daughter carries a cystic fibrosis mutation.
Which one of the following is the correct answer?