A Genetics question I can't figure out, HELP Please!

[007Dabomb]

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Cystic Fibrosis AR (or any other gene defect for that matter)

Father has both normal genes
Mother is a carrier for CF
Kid is affected.

How?

 

[Pinkertinkle]

Mommy cheated on daddy.

 

[WhoisJohnGalt]

Mommy cheated on daddy.

True, but you should probably tell them it was a spontaneous mutation 😉

 

[mohaven]

Mommy cheated on daddy.

 

[mudphudwannabe]

Our genetics prof was obsessed with nonpaternity. I think he said the rate was as high as 5%. Anyway, probably higher than the rate of spontaneous mutation...

 

[007Dabomb]

Are there many questionable paternity stuff on Step 1? What are kinds of genetics topics they test?

 

[blz]

Are there many questionable paternity stuff on Step 1? What are kinds of genetics topics they test?

the inheritence questions are so rediculously easy on the test. i think the hardest one i saw was mitochondrial inheritance. they're not gonna pull a cheating mom on you.

 

[SeventhSon]

mosaicism?

 

[Mike Jones]

Mother gave both copies of the gene, father contributed none, i forget the name but it is also a cause of Angelmans/prader wili

 

[cdql]

Mother gave both copies of the gene, father contributed none, i forget the name but it is also a cause of Angelmans/prader wili

Hmm...imprinting plays a role in CF? I didn't know that

 

[mudphudwannabe]

I think what Mike Jones is referring to is uniparental disomy -- where both copies of one chromosome come from one parent. It is a possible explanation, although it seems somewhat unlikely. Imprinting is why there are 2 different syndromes (Prader Willi and Angelman's) depending on which parent the chromosome came from when the same chromosomes are involved. As far as I know, imprinting doesn't play a role in CF.

Gonadal mosaicism of the father is possible, but I'm not sure what the probability of that is. I'd still guess spontaneous mutation or non-paternity are the most likely. If this were a real question on the boards, the answer choices would probably not be so tricky. I don't think there was any non-paternity stuff on my exam. It would have cracked me up for sure. 👍

 

[Miami_med]

I actually did have a question where non-paternity was a potential answer. For this particular question, I thought he was the father.