Dear Hannah,
CF is caused by having 2 copies of the "CF" gene that have CF mutations. Each person has two. You mom has two, one with a mutation and one without. Your dad has two, one with a mutation and one without. You received one gene from your mom and one from your dad. You receive the one from your mom that had the CF mutation and you received the one from your dad with the CF mutation. Your sibblings may have received one CF mutation from either your mom or your dad, but then they received one without a mutation from the other--or they received one mutation from each without mutations. If they are tested, they would then know if they are "carriers," meaning they have one CF gene. Both of your parents are CF carriers. There is a 25% chance for each child to have CF because there are 4 different possibilities for each child: 2 normal; 2 CF; 1 normal from mom and 1 CF from dad; and 1 CF from mom and 1 normal from dad. There is no way to determine which you'll get, just like eye color. hugs
