Answer to Question #306321 in Genetics for love

Question

1. A woman's sister has cystic fibrosis, a disease caused by recessive genes. Neither of her parents has the disease. What chance is there that her mother is a carrier (heterozygous) for the trait? What chance is there that the woman herself is a carrier for the trait?  

2. Huntington's disease is a degenerative disease of the nervous system which does not show up until age 40. It is caused by a dominant gene. John's father just began to show the symptoms. What is the chance that John will have the disease?

Answer 1

An individual must inherit two non-functioning CF genes – one from each parent – to have CF. If both parents are carriers there is a 1 in 4 (25 percent) chance that both will pass on the non-functioning gene, which would result in a pregnancy affected with cystic fibrosis.