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NBME 23 Answers

nbme23/Block 1/Question#26

A couple comes to the physician for counseling ...

1/150

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2/3 1/25 1/4

He has a 2/3 chance of being heterozygous (not 2/4 b/c we know he for sure doesn't have CF)

1/25 chance in the population

1/4 chance of a heterozygous couple having a child with CF

welpdedelp  ok, so it messed up the formatting 0.66667 x 1/25 x 0.25 +  
nwinkelmann  ugh... I ALWAYS forget about changing the carrier status to 2/3. Chance of affected individual = chance of father passing allele * chance of mother passing allele = 2/31/21/25*1/2 = 2/300 = 1/150. +  
zpatel  2/3(chance of heterozygous) * 1/25(meet carrier) * 1/2(chance of male to transfer affected gen) * 1/2(female to transfer affected gen) = 1/150 +