Can you determine if CF is dominant or recessive? explain.?

Question

Elizabeth and Peter are a young married couple expecting first child. Elizabeth has a sister with cystic fibrosis (CF), they are concerned there is a possibiity that their child may also inherit the disease. Can you determine if CF is dominant or recessive? explain.

Answer 1

CF is an autosomal recessive disease. To suffer from CF you must inherit a mutant copy of the gene from each parent (excluding the chance of new mutation as the probability is very low),

If Elizabeths sister suffers from CF then her parents are both obligate carriers of CF. The Chance of Elizabeth being a CF carrier is 2/3 (basic mendelian genetics). Without any information about Peter's carrier status he is assumed to have a population risk of being a carrier, in the case of CF the population risk is approx. 1/22.
The probability of the expected child being a CF sufferer can be calculated as being 1/132 (1/22 x 2/3 x 1/4).

If CF was a dominant mutation then for the expected child to inherit the disease then at least one of the parents must also be a sufferer (this does not apply to X-linked disorders). The question does not say that elizabeth suffers from CF so you can assume that it is not a dominant mutation from this information.

For confirmation, both of the parents can be tested for CF carrier status and in the event that both parents are carriers, prenatal testing is available for CF.

Answer 2

You can't from the information you have given. You need to know if Elizabeth's parents had CF.

Answer 3

Let her give birth then you can say final bcos it may be dominant or recessive .

Answer 4

http://www.cysticfibrosis.org.au/aboutcf/whatis/