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What is the risk that Jill is a carrier for the disease allele?

Jack and Jill who are both 30 years old want to have a baby.

Jill’s sister has a child with cystic fibrosis.

What is the risk

that Jill is a carrier for the disease allele?

I know cystic fibrosis is AR however how can I know for sure the risk for Jill of being a carrier is 50%?

1 Answer

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  • 7 years ago
    Favorite Answer

    For her sister to have the disease BOTH parents must be carriers.

    The risk of inheriting the disease from either parent is 50%

    To develop CF you have to inherit from both parents so risk is 50% x 50% or 25%

    The chance of NOT being a carrier or having the disease means you inherit from neither parent so 50% x 50% or 25%

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