Phenylketonuria and genetics - USMLE Forums
 USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
 Home USMLE Articles USMLE News USMLE Polls USMLE Books USMLE Apps
 USMLE Forums Phenylketonuria and genetics
 Register FAQs Members List Search Today's Posts Mark Forums Read

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

#1
05-30-2011
 USMLE Forums Addict Steps History: 1 + CS Posts: 113 Threads: 8 Thanked 89 Times in 61 Posts Reputation: 99
Phenylketonuria and genetics

A man with phenylketonuria (PKU) is planning to start a family with his healthy, unaffected & unrelated partner, who has no family history of PKU. PKU shows autosomal recessive inheritance with an incidence of 1 in 10 000. Assume that the population is in Hardy-Weinberg equilibrium. Which of the following is correct?

a) The probability that his partner is a carrier is 1 in 100.
b) The probability that the man will transmit a mutant allele to his first child is 1 in 2.
c) The probability that his partner will transmit a mutant allele to their first child is 1 in 50.
d) The probability that their first child will be affected is 1 in 100.
 The above post was thanked by: bebix (05-30-2011), intellijem (07-24-2014), usluipek (05-30-2011)

#2
05-30-2011
 USMLE Forums Guru Steps History: --- Posts: 332 Threads: 48 Thanked 170 Times in 109 Posts

affected rate is 1/100000
mutant allel frequecy is 1/100
carrier rate is 2/100 (the man's partner)
chances of passing a mutant allel to child is 1/100
 The above post was thanked by: Claus_CU (05-30-2011)
#3
05-30-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,269 Times in 881 Posts Reputation: 3279

Quote:
 Originally Posted by Claus_CU A man with phenylketonuria (PKU) is planning to start a family with his healthy, unaffected & unrelated partner, who has no family history of PKU. PKU shows autosomal recessive inheritance with an incidence of 1 in 10 000. Assume that the population is in Hardy-Weinberg equilibrium. Which of the following is correct? a) The probability that his partner is a carrier is 1 in 100. b) The probability that the man will transmit a mutant allele to his first child is 1 in 2. c) The probability that his partner will transmit a mutant allele to their first child is 1 in 50. d) The probability that their first child will be affected is 1 in 100.
HW eq.
carrier = 1/50
If the partner is a carrier= 50% children normal - 50% with PKU

then, probability that their first child will be affected
1/50 * 1/2 = 1/100

 The above post was thanked by: Claus_CU (05-30-2011)

#4
05-30-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,175 Threads: 38 Thanked 854 Times in 478 Posts Reputation: 864

Quote:
 Originally Posted by Claus_CU A man with phenylketonuria (PKU) is planning to start a family with his healthy, unaffected & unrelated partner, who has no family history of PKU. PKU shows autosomal recessive inheritance with an incidence of 1 in 10 000. Assume that the population is in Hardy-Weinberg equilibrium. Which of the following is correct? a) The probability that his partner is a carrier is 1 in 100. b) The probability that the man will transmit a mutant allele to his first child is 1 in 2. c) The probability that his partner will transmit a mutant allele to their first child is 1 in 50. d) The probability that their first child will be affected is 1 in 100.
D) The probability that their first child will be affected is 1 in 100.

Incidence is 1/10000 = 1%

If the affected individual has one mutant allele (1/2), and he is mating with a homozygous normal (0/2) individual, the chances are the same as amongst the general population.
 The above post was thanked by: Claus_CU (05-30-2011)

 Tags Biochemistry-, Genetics-, Step-1-Questions

Message:
Options

## Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
User Name:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
 AMG IMG ---
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

 Not yet Step 1 Only CK Only CS Only 1 + CK 1 + CS 1+CK+CS CK+CS 1+CK+CS+3 ---
Favorite USMLE Books
 What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
 Where you live. Leave blank if you don't want to tell.

## Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.