A- 0.09

B- 0.07

C- 0.05

D- 0.025

E- 0.25

F- 0.50

G- 0.10

1 - 13 of 13 Posts

A- 0.09

B- 0.07

C- 0.05

D- 0.025

E- 0.25

F- 0.50

G- 0.10

Please tell me how did u arrive to this conclusion!i think the answer is E

married to affected homozygous 1%

married to affected heterozygous (should be calculated by Hardy weinburg)

married to homozygous normal person (the remaining possibility)

These probabilities should be combined

If some one can do the math for us to know the answer

its C 0.05

disease prevalence 1% = 1/100 = q2

allele frequency = q = 1/10

when disease frequency is less then 1/100 p(normal allele frequency) is considered 1

so....carrier frequency will be 2pq = 2q = 1/5

for AR disease , father must be carrier to transmit disease to child...

probability that women will marry carrier man is 1/5

probability that women will transmit her diseased allele to child is 1/2

probability that man will transmit his diseased allele to child is 1/2

now just multiply 1/5*1/2*1/2 = 1/20 = 0.05

I did it a bit differently as I included the likelyhood of marrying a homozygous ressessive and having a child (ended up being .005)

I also didn't assume p as being 1 (rather .9) so i got .045 instead of .05

The grand total was .05.

I guess either way works.

I have a doubt..is the probability of man transmitting the dz is 1/4 coz the question says the woman will marry a guy from homozygous population??its C 0.05

disease prevalence 1% = 1/100 = q2

allele frequency = q = 1/10

when disease frequency is less then 1/100 p(normal allele frequency) is considered 1

so....carrier frequency will be 2pq = 2q = 1/5

for AR disease , father must be carrier to transmit disease to child...

probability that women will marry carrier man is 1/5

probability that women will transmit her diseased allele to child is 1/2

probability that man will transmit his diseased allele to child is 1/2

now just multiply 1/5*1/2*1/2 = 1/20 = 0.05

Can anybody explain this question again?

may i suggest another solution

since 1% of that population is homozygous normal or diseased

if the woman marries a homozygous normal from that 1% she wont get a diseased homozygous baby

if she marries a homozygous diseased person from that same 1% she will get a homozygous diseased baby but for our calculation purpose we are going to neglect that homozygous diseased population since it will be negligible as it is an AR disease and it will be a small fraction of that 1%

so the probabability of that woman marrying a heterozygous carrier is 99% or 0.9

the probability of her having a homozygous diseased baby if she marries a heterozygous carrier = 1/4 or 0.25

the probability of husband having a homozygous diseased baby if he marries a heterozygous carrier = 1/4 or 0.25

multiply all the probabilities

0.9 x 0.25 x 0.25 = 0.05

Probability of a homozygous child if someone

Now by

Situation 1 - Another carrier from the population marries Miss X. The probability of this event happening is - 2pq = 2x0.9x0.1 = 0.18 (Note: the square of q = 0.01, hence 1=0.1 and p=1-0.1 = 0.9. We can't ignore p in the equation because the prevalence is high.)

Now if this mating occurs, probability of having a homozygous child = 0.25 (draw a punnet square if you please.)

Hence combining the probabilities, final probability from situation 1 = 0.18x0.25 =0.45.

Situation 2 -A homozygous diseased male marries Miss X. Note that the question doesn't suggest that the female will only marry a phenotypically normal guy. The probability of this event happening is 0.01 (frequency of homozygotes is given in the question as 1%).

If this mating occurs, probability of having a homozygous child = 0.5.

Combined probability from situation 2 = 0.05.

Now to calculate the final answer, we must understand that

So combining situation 1 and 2, final probability = 0.45 + 0.05 = 0.5

I know this is confusing and we probably won't be tested such complicated applications but once you read it slowly and refer to your genetics book, you would get it. I think a similar questions can be found in the Kaplan qbank. Hope that helped.

1 - 13 of 13 Posts

Join the discussion

USMLE Forums

A forum community dedicated to the United States Medical Licensing Examination. Come join the discussion about schools, exams, news, prep, reviews, accessories, classifieds, and more!

Full Forum Listing
Recommended Communities

Join now to ask and comment!