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NBME 19 Answers

nbme19/Block 3/Question#19 (reveal difficulty score)
30 yo man and 24 yo woman; best estimate that ...
1 in 600 🔍 / 📺 / 🌳
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shadowbox on 1 in 600

 +11 
submitted by shadowbox(17),
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cSien hte s'freath bingisl si ctaeed,ff ew wnok ttha eth tashef'r pnerast rea htbo rsr.irace Ttha names hte sseolipb tnpgsyeeo fo the efhrta are AA, ,Aa Aa, ro aa.

eW nowk het fareht si fcfauedtn,e os ttah asmne eh nonact be ,aa adn sutm eb htiree A,A A,a or Aa.

cnSei erhte ear nyol 3 trdeifnfe ysnopgeet he odcul ,vhae itwh 2 fo ethm gbine rreciar gty,osneep ehter is a /32 byobiraiplt eh is a ie.arrcr

So we tinboa het iipyatrolbb of eth ftraeh ssipang on a essreevic elelal sa 3/2 bp(tayiboirl of nigbe a rire)cra x 2/1 bpbyrila(oti fo npigssa no a cesvsreie leelal fi he is a )ieac.rrr hTe /32 is ton aevrlnet to hte aibrotpylbi atth the omreth is a rirr.eac

We wkno the furqnecey fo cfatdefe uadnlviisdi ni eht oapoiultnp ta lrega is ,00/0041 2,)q(=^ so 02/q0=1.

P=q,+1 so p21900=9/ and )911)(00/q22(2=0p9./20

To aekm iimntoalcpilut seiaer we essmua 00=12919,/ os:

=*1=010/2021)q/02p( ;>-- hsti si teh rcirare ecfqeurny a.,(ka.. tgohe)reytsezo in hte uoptp,alnio ichwh we anc essuam rof eth meo.hrt

So, ot aernws teh nerite tesiuqno we yiplmlut eht rbioapitbly tath tfeahr is a rciearr )(3/2 dan spesas no het llelea 2()/1 iestm hte lbatoyirpib ttha oemhrt si a rarierc 1(/0)01 adn ssaspe on het lleael /;12() gtutnpi it all egehtort we ehv:a

/(1)0()321*/)*21021(/()/* = 0221/0 = 0/601

cbay0509  thank you +  
garble  Why is it assumed that the mother is a carrier? Couldn't it also be possible the mother is unaffected and not a carrier? +1  
garble  Turns out the difference is negligible, nevermind. +  
chaosawaits  Who added all these questions with abbreviated stems? fml +  
chaosawaits  The chance of the mother being a carrier is 2/3 because she's obviously not homozygous (so there are only three possibilities for her, 2 of which she is a carrier). Take the square root of 40,000 to get q = 200. (2/3) * (1/2) * 200 = 600 +1  
neurotic999  For people like me who royally messed up: Probability that the father is a carrier 2/3 (since we know he isn't affected i.e he isn't aa. So only things he could be are AA, Aa & aA. 2 of the 3 options are carrier states) Probability that he passes the gene 1/2 Probability that the mother is a carrier-->2pq. q^2=1/40,000. q=1/200. 2pq=1/100 (considering p as 1) Probability that she passes the gene 1/2 2.3 x 1/2 x 1/100 x 1/2 = 1/600 +  
neurotic999  For people like me who royally messed up: Probability that the father is a carrier 2/3 (since we know he isn't affected i.e he isn't aa. So only things he could be are AA, Aa & aA. 2 of the 3 options are carrier states). Probability that he passes the gene 1/2. Probability that the mother is a carrier-->2pq. q^2=1/40,000. q=1/200. 2pq=1/100 (considering p as 1). Probability that she passes the gene 1/2. 2/3 x 1/2 x 1/100 x 1/2 = 1/600 +  



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