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  #1  
Old 05-31-2011
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Cool If you don't die after this...you're done with genetics!

Subject I 1 and II 2 have Becker muscular dystrophy (X-linked recessive inheritance)
Subject III 2 has oculocutaneous albinism (autosomal recessive inheritance, incidence in the general population of 1/10 000.
The disease status for both Becker muscular dystrophy and oculocutaneous albinism is unknown for IV 1 and IV 2.

If you don't die after this...you're done with genetics!-usmle-pedigree.jpg
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1) What is the probability that III 3 is a carrier of Becker muscular dystrophy?
a) 1/4
b) 2/3
c) 1/2
d) 1

2) What is the probability that III 3 is a carrier of oculocutaneous albinism?
a) 1/4
b) 2/3
c) 1/2
d) 1

3) What is the probability that IV 1 is a carrier of oculocutaneous albinism?

a) 1/4
b) 1/2
c) 2/3
d) 99/100

4) What is the probability that IV 2 will be affected with Becker muscular dystrophy?

a) 1/4
b) 1/2
c) 0
d) 1

5) What is the probability that IV 2 will be affected with oculocutaneous albinism?

a) 1/100
b) 1/50
c) 1/24
d) 1/12

Have fun
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  #2  
Old 05-31-2011
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Default Answer

those questions were some how confusing
these are my answers by the way:
1- a
2- b
3- a
4- a
5- d

how many of them are correct & how many wrong??
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  #3  
Old 05-31-2011
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1 - d
2 - c
3 - d
4 - b
5 - a
Please tell the correct answers.

Last edited by maitribhandari; 05-31-2011 at 12:00 PM.
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  #4  
Old 05-31-2011
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Default My answers

Wow great question.

Here are my answers -

1) What is the probability that III 3 is a carrier of Becker muscular dystrophy?
a) 1/4
b) 2/3
c) 1/2
d) 1

2) What is the probability that III 3 is a carrier of oculocutaneous albinism?
a) 1/4
b) 2/3
c) 1/2
d) 1

3) What is the probability that IV 1 is a carrier of oculocutaneous albinism?

a) 1/4
b) 1/2
c) 2/3
d) 99/100

4) What is the probability that IV 2 will be affected with Becker muscular dystrophy?

a) 1/4
b) 1/2
c) 0
d) 1

5) What is the probability that IV 2 will be affected with oculocutaneous albinism?

a) 1/100
b) 1/50
c) 1/24
d) 1/12

I guessed on the last one! Hope Im right. Im quite weak in genetics though! Looking forward to your answers and explanations.
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  #5  
Old 05-31-2011
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Not to offend the OP, but this question really sucks cause the pedigree doesn't distinguish if the mother/father/grandfather/grandmother is a carrier or not.. so you're made to assume.

1) C
2) C
3) A
4) C
5) C
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  #6  
Old 05-31-2011
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haha

Actually, ALL the info is there...this is what you know:
"Subject I 1 and II 2 have Becker muscular dystrophy (X-linked recessive inheritance). Subject III 2 has oculocutaneous albinism (autosomal recessive inheritance), incidence in the general population of 1/10 000.
The disease status for both Becker muscular dystrophy and oculocutaneous albinism is unknown for IV 1 and IV 2."

the rest is just pure probabilities (if the subject is or not a carrier is indeed a probability)

have fun!

Last edited by Claus_CU; 05-31-2011 at 12:45 PM.
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  #7  
Old 05-31-2011
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Show Teeth

1) D
2) B
3) D
4) B
5) C?



I think Im gonna die now, hahaha
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  #8  
Old 05-31-2011
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Correct Answer correct answer

The correct answer are:

1) What is the probability that III 3 is a carrier of Becker muscular dystrophy?
a) 1/4
b) 2/3
c) 1/2
d) 1

2) What is the probability that III 3 is a carrier of oculocutaneous albinism?
a) 1/4
b) 2/3
c) 1/2
d) 1

3) What is the probability that IV 1 is a carrier of oculocutaneous albinism?

a) 1/4
b) 1/2
c) 2/3
d) 99/100

4) What is the probability that IV 2 will be affected with Becker muscular dystrophy?

a) 1/4
b) 1/2
c) 0
d) 1

5) What is the probability that IV 2 will be affected with oculocutaneous albinism?

a) 1/100
b) 1/50
c) 1/24
d) 1/12

Thanks everybody!
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  #9  
Old 05-31-2011
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1. D
2. C
3. D
4. B
5. C
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  #10  
Old 05-31-2011
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@awaisnaeem86 check the right answers above
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  #11  
Old 05-31-2011
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BTW:

check this link for the explanations
Also you'll find more questions!

http://www.oup.com/uk/orc/bin/978019...ces/risk/quiz/
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  #12  
Old 05-31-2011
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WOW..shoot me now!
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  #13  
Old 05-31-2011
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i dint understand the Q.NO 23 n 25 ANSWERS.......
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  #14  
Old 05-31-2011
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Wink Question 23 (aka 3)

Quote:
Originally Posted by sana akbar View Post
i dint understand the Q.NO 23 n 25 ANSWERS.......
Question 23 (aka 3)
probability that IV 1 is a carrier of oculocutaneous albinism?

Father aa
Mother Aa or AA
Probability Mother is a carrier
Incidence = 1/10000 = p^2 => p=1/100
HW eq = 2pq = 1/50
Probability Mother not carrier
1-1/50

Then
If mother is a carrier Aa + Father aa
aa aa Aa Aa = 1/2 * 1/50 "IV 1 is a carrier"
If mother is NOT a carrier AA + Father aa
Aa Aa Aa Aa = 1 * 49/50

Then, probability that IV 1 is a carrier of oculocutaneous albinism
= 1/100 + 49/50 = 99/100
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  #15  
Old 05-31-2011
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Wink Question 24 (aka 4)

Question 24 (aka 4)
What is the probability that IV 2 will be affected with Becker muscular dystrophy? X-linked recessive

Father X_A Y
Mother X_A X_a (her Father has the disease)

Posible son if Mother X_A X_a:
X_A Y
X_a Y

Then, probability that IV 2 (male) will be affected with Becker muscular
1/2
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  #16  
Old 05-31-2011
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Question 25...I'm still trying to understand the qs...
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  #17  
Old 05-31-2011
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Wow! Got 3 out 5 .. Not bad!! This was a confidence booster for genetics lol .. but to expect these kinda questions i clearly need wayyy more practice and need to go over everything again!
Thanks for sharing.
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  #18  
Old 05-31-2011
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Wink Question 25 (aka 5)

Question 25 (aka 5)

What is the probability that IV 2 will be affected with oculocutaneous albinism?
We know from qs. 22 (2) that the probability that III 3 is a carrier of oculocutaneous albinism is 2/3.
We also know that II 3 must be a carrier, then the probability that subject II 4 is a carrier is 1/2 (mother & father both carrier OR one of those is carrier and the other is normal)
Now we have to calculate the probability that the subject III 4 is also a carrier.

Using degree of inbreeding (the degree of risk that both alleles of a pair in a person are descended from the same recent common ancestor) the probability that the subject III 4 is also a carrier is 1/2 * 1/2.

If subject III 3 & III 4 are carriers, we'll have:
AA Aa Aa aa

Finally, putting everything together we have:

2/3 (mom) * 1/4 (dad) * 1/4 (aa) = 1/24
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  #19  
Old 06-01-2011
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hi bebix ...
thanks for the reasoning ... good one
but i have hard time to understand q 25 line
" We also know that II 3 must be a carrier, then the probability that subject II 4 is a carrier is 1/2 (mother & father both carrier OR one of those is carrier and the other is normal)"
please explain in detail ... thanks
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  #20  
Old 06-01-2011
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Quote:
Originally Posted by amritdhillon257 View Post
hi bebix ...
thanks for the reasoning ... good one
but i have hard time to understand q 25 line
" We also know that II 3 must be a carrier, then the probability that subject II 4 is a carrier is 1/2 (mother & father both carrier OR one of those is carrier and the other is normal)"
please explain in detail ... thanks
Since subject III2 has this autosomal recessive disease (aa), then subjects II 2 (father) & II 3 (mom) must be carriers.

So II 3 must be Aa
Now, her brother (II4) has a 1/2 probability of being a carrier too:
- if mom & dad are are carrier (Aa * Aa = AA Aa Aa aa)
- if one is carrier and the other is not (AA * Aa = AA Aa AA Aa)
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Old 06-01-2011
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thanks bebix its working ....
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  #22  
Old 06-04-2011
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OMG!!! is this for real?
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  #23  
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Default Thanks a lot ...

Quote:
Originally Posted by Claus_CU View Post
Subject I 1 and II 2 have Becker muscular dystrophy (X-linked recessive inheritance)
Subject III 2 has oculocutaneous albinism (autosomal recessive inheritance, incidence in the general population of 1/10 000.
The disease status for both Becker muscular dystrophy and oculocutaneous albinism is unknown for IV 1 and IV 2.

Attachment 1401
click image to enlarge

1) What is the probability that III 3 is a carrier of Becker muscular dystrophy?
a) 1/4
b) 2/3
c) 1/2
d) 1

2) What is the probability that III 3 is a carrier of oculocutaneous albinism?
a) 1/4
b) 2/3
c) 1/2
d) 1

3) What is the probability that IV 1 is a carrier of oculocutaneous albinism?

a) 1/4
b) 1/2
c) 2/3
d) 99/100

4) What is the probability that IV 2 will be affected with Becker muscular dystrophy?

a) 1/4
b) 1/2
c) 0
d) 1

5) What is the probability that IV 2 will be affected with oculocutaneous albinism?

a) 1/100
b) 1/50
c) 1/24
d) 1/12

Have fun

My genetics professor had fun giving us this to play with a week before midterms...
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