A son with cystic fibrosis (autosomal recessive) is born to a couple who appears to be normal. What are this couple's chances of having a child with cystic fibrosis?

Question

shrutipande9 · Answer

hi aroub.....can u tell me the genotype of the son...can u guess that?

aroub · Answer

aa?

abhisar · Answer

Hello ^_^

aroub · Answer

Hiiii

abhisar · Answer

Cystic fibrosis is a rcessive disease.

shrutipande9 · Answer

yes great...now can u guess what all possibilities of genotypes are there for normal?

aroub · Answer

For the normal, Aa, AA or A? I'd go with the A? because we don't know the other one, but then what? :/

shrutipande9 · Answer

A only? genotype has to be with 2 alleles...
so the first two are right...AA and Aa. Now if the both parents are AA. they wudnt have a recessive allele and so their son has to be normal...

abhisar · Answer

If you assume it to be AA, then no offspring will have cystic fibrosis because it's a recessive disease and needs to have aa in order to express.

shrutipande9 · Answer

we r explaining the same thing in the same way.:P

aroub · Answer

No :p I meant A? (One allele unknown)

abhisar · Answer

Let's see
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abhisar · Answer

See all will have a dominant allele and hence no offspring will have the disease.

Shruti :O (I know you are the best ;))

aroub · Answer

So, it's Aa x Aa

abhisar · Answer

Aroub, are you getting?

Or have I confused you more? :O

aroub · Answer

so 25% chance?

aroub · Answer

No, I think I got it :p Thank you both!!