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How do parents who do not have cystic fibrosis produce a child who has cystic fibrosis?

In: Conditions and Diseases, Genetics, Cystic Fibrosis [Edit categories]

Answer:

"Cystic fibrosis (CF) is an autosomal recessive disease. That means that if both parents have cystic fibrosis, so will any children that they have. If one parent has cystic fibrosis and the other does not, then the chance drops dramatically (almost to zero)."

Not wholly correct. CF is a recessive disease which means that you must posses two copies of the faulty gene (1 from your mother and 1 from your father) in order to present with the condition. If one parent has CF then the chances of them presenting with the disease are as follows.

If the other parent also has CF, then 100% as you stated
If the other parent is a carrier (has one Normal gene and one faulty gene) then there is a 50% (not almost 0%) chance that the child will have CF, and if not, they will be a carrier.
If the other parent doesn't have CF and doesn't carry the faulty gene. Then the child will not have CF but will be a carrier.

The original question was how can two parents who do not have CF produce a child that has CF. In this instance, both parents have to carry the recessive gene, but it doesn't present in them because the gene is recessive, it is overruled by the dominant, normal gene. Using a genetic cross diagram known as punnett square, we can work out that there will be a 25% chance of the child between the two parents who carry the faulty gene, inheriting CF, a 50% chance they will be a carrier, and a further 25% chance that they will neither have the disease or be a carrier.

Furthermore, CF also effects the reproductive system (predominantly in males i believe), so many sufferers are unable to have children.

First answer by Erythropoietin. Last edit by Matt Robertshaw. Contributor trust: 0 [recommend contributor ]. Question popularity: 1 [recommend question].

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Relevant answers:

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