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NBME 21 Answers

nbme21/Block 4/Question#39

A 46-year-old man comes to the physician because of ...

1/15

A 46-year-old man comes to the physician because of ...

1/15

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arkmoses
You have to use the hardy weinberg formula (1=p^2+2qp+q^2)and p + q = 1 they basically tell you that q^2=1/900 which makes q=1/30 now you can figure out (p=1-q) so p=1-(1/30), p=29/30 then to figure out carrier you solve for 2qp, 2(29/30)(1/30)=1/15 I got it wrong cuz I forgot how to figure out p but hopefully wont happen on the real deal.
+3

pg32
How do we know this disease is autosomal recessive? I assumed it was just because they love these carrier frequency questions with AR diseases, but how do we know it's AR?
+

p^2 + 2pq + q^2 = 1 p+q= 1

q^2= 1/900 q= 1/30 p= 29/30 which rounds to 1

They are asking for carrier frequency which is 2pq.

q^2 = 1/900 --> q = 1/30

Carrier frequency per Hardy-Weinberg formula is 2pq.

Now, for *rare* autosomal recessive diseases the carrier frequency of 2pq ≈ 2q.

2q = 2(1/30) = 2/30 = 1/15

Answer = 1/15

Where is this even from? My mind's going hay wire trying to understand this.

sahusema
Hardy Wineberg equilibrium
square root 900 = 30
1/2 of all offspring will be carriers so 30*.5 = 15
simple as that
+4

If u are not goot in math like me xD. I did it this way: They gave me p^2=1/900 so p=1/30.

Now I need to find P, so use p+q=1. p= 1-(1/30)= 1-0.03= 0.97

So, 2pq= 2(0.97)(0.03)= 0.064 = (1/15) :D I got it right, this is my way to do it cause im not good at fractions.

submitted by taway(8), 2019-06-03T20:41:50Z

Just as a note for anybody else who was WTF at how 2(29/30)(30/30) = 1/15...a lot of question banks round 29/30 (or any similarly large fraction) out to 1