








USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam 

Thread Tools  Search this Thread  Display Modes 
#1




Hardy Weinberg Genetics
Clearly I fell asleep in genetics when we learned this. now its coming back to haunt me. IM lost and would like someone to teach me how to solve questions like these. PLEASE
In a small city with a stable Caucasian population, the carrier frequency of cystic fibrosis is 1/30. In a nearby community, the cystic fibrosis carrier frequency in Asians is 1/100. What is the probability that a child born to a mother from the Caucasian community and a father from the Asian community will suffer from the disease? 
The above post was thanked by:  
neha_subh (04052013) 
#2




For probability questions you have to multiply....
Since cystic fibrosis is an Autosomal Recessive condition, both parents must carry the allele to pass it on to the next generation. If either parent is a carrier, the probability that the child will inherit the mutant allele is 1/2. So Mother= 1/2 * 1/30 Father= 1/100 * 1/2 1/60 * 1/200 answer: 1/12000 
#3




Mmm.. doesn't this answer only assume if the parents were only carriers? Don't we have to account for if the homozygous recessive parents were to meet?
ie. Carrier = 1/30 = 2pq Homozyg Recess = 1/60 Then you have to calculate total probability of a Carrier from the caucasian community, with a carrier from asian, or with a homozygous recessive from asian, and vv? I feel like we completely ignored the homozygous recessive. Can someone double check me? 


#4




chances of mother being carrier = 1/ 30
chances of father being carrrier =1/100 chances of 2 carrier mating n produciing affected child = 1/4 therefore chances of child being affected is = 1/4* 1/30* 1/100 = 1/12000 
The above post was thanked by:  
neha_subh (04052013), roopa.loveurlife (05242013) 
#5




Again... what about the homozygous recessive? Is this kind of a question assuming that both of the parents are only carriers, and can't be homozygous recessive?
Carrier frequency is only telling us 2pq (heterozygous) and nothing about q2 isn't it? Thanks! 
#6




If they are homozygous recessive,then they clearly mention thier phenotype(affected with CF)..In the above question,they didnt mention any such,so we hav to consider they are phenotypically normal(can be homozygous for normal allele or heterozygous for mutant alelle ). Thus u calculate carriers who appear phenotypically normal and their chance of producing affected child.

#7




Quote:
that is why u multiply the carrier frequency by 1/2=chance of carrier mom or dad giving affected gene if it was q2 or (disease frequency)than there would be no need for multiplication by 1/2
__________________
Everything is possible for him who believes (MARK 9:23) 245/247/passed on 1st attempt/223/2mos Obsie /3 US LORS/visa not needed/2008 grad 
Tags 
Genetics, Step1Questions 
Thread Tools  Search this Thread 
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
HardyWeinberg in AD, X linked  inno  USMLE Step 1 Forum  0  09202012 04:35 AM 
HardyWeinberg Allele value?  Renaissance  USMLE Step 1 Forum  10  04222012 07:05 PM 
geneticsHardy weinberg question  drgsarunprasath  USMLE Step 1 Forum  4  08102011 07:37 AM 
HardyWeinberg equation help  docnas  USMLE Step 1 Forum  1  01212011 07:43 AM 
Hardy weinberg equation!!!  fauzan  USMLE Step 1 Forum  7  12302009 12:23 PM 
