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#1
04-18-2014
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 148 Threads: 37 Thanked 73 Times in 57 Posts Reputation: 83
genetics:Question doubt?

An causian man and woman are affected with autosomal dominant disease that has 80% penetrance in all individuals.They are both heterozygotes for the disease causing mutations.what is the probabilty they with produce a phenotypical normal offspring?

1.20%
2.60%
3.25%
4.40%
5.70%

can someone explain this question..i got the answer as 20% ...after i got 1/4 in punett square i multiplied it with 80% to include penetrance....but the answer key states the answer is 40%...can someone explain thank u...

#2
04-18-2014
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 148 Threads: 37 Thanked 73 Times in 57 Posts Reputation: 83

#3
04-18-2014
 USMLE Forums Addict Steps History: 1+CK+CS+3 Posts: 117 Threads: 3 Thanked 50 Times in 41 Posts Reputation: 60

with 80% penetrance, the probability for the offspring to be affected in this case is: 0,75x0.8=60% . So it also mean, out of the 75 % theorically affected, 15% will not be phenotypically affected. You add this 15% to the 25% who are free of any risk to be affected, and you get 40%. The key here is to remember that inside the ones who have the gene, you have some who will not phenotypically express the disease, I think... Hope that's help...
 The above post was thanked by: dr rookie (04-18-2014), hope2015 (04-19-2014), placebo (04-20-2014)
#4
04-19-2014
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 148 Threads: 37 Thanked 73 Times in 57 Posts Reputation: 83
@ramennoodles

thanks a lot
 The above post was thanked by: ramennoodles (04-20-2014)

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