NBME 24 X-linked recessive (NBME Answers)

You must be logged in to vote!
You must be logged in to vote!

Retired NBME 24 Answers

nbme24/Block 1/Question#5 (reveal difficulty score)
The 35-year-old woman indicated by the arrow ...
X-linked recessive 🔍 / 📺 / 🌳 / 📖
tags: genetics process_of_elimination

+16 upvote downvote
submitted by stars and more(16)

get full access to all content ⋅ pick a username

X linked recessive there can never be any Male to Male transfer since the male offspring gets Y from father. the pedigree shows Male to Male transmission so this cannot be X linked recessive

get full access to all content ⋅ pick a username

weirdmed51 ??? +

weirdmed51 The pedigree shows only affected male, hence there has been female to male transmission (females-carriers). Hence X linked recessive. +

weirdmed51 Nevermind, I got it wrong. +1

freemanpeng I beg to differ... AR is much more unlikely than XR in this case. 1. XR, you only need 2 carrier wivies 2. AR, you need(1)2 carrier wives and(2)only boys inherited that mutated gene. Poor NBME guys, knowing nothing about maths, only sticking to stupid "Male to Male transmission" law +

You must be logged in to vote!
You must be logged in to vote!

+15 upvote downvote
submitted by ∗monoclonal(24)

get full access to all content ⋅ pick a username

The point here is, they are asking us to eliminate the only answer that is not possible. I got it wrong. read well fellas

get full access to all content ⋅ pick a username

ergogenic22 nbme logic: "what if they all marry carrier wives" And doesn't everyone with autosomal dominant get it in the 2nd generation (unless incomplete penetrance) i feel dumb +26

cavernosum totally agree. what a st*pid qs! +1

You must be logged in to vote!
You must be logged in to vote!

+6 upvote downvote
submitted by obgynnycstep1(7)

get full access to all content ⋅ pick a username

The pedigree presents us with Male-to-Male transmission. There are two modes of inheritance where Male-to-Male transmission is impossible: 1) X-linked recessive 2) Mitochondrial inheritance

get full access to all content ⋅ pick a username

You must be logged in to vote!
You must be logged in to vote!

+2 upvote downvote
submitted by trazabone(16)

get full access to all content ⋅ pick a username

My understanding is that if parents are unrelated by blood to those affected, we assume that they are not carriers (in the recessive case). Therefore, if we have a male father affected with x-linked recessive married to a non-carrier, there's no way any of his offspring would be affected.

"If one parent is not a carrier, then a child can only inherit a disease allele from the other parent. In these problems, we can assume that any individual marrying into the family is not a carrier." https://www.cs.cmu.edu/~genetics/units/instructions/instructions-CP.pdf

get full access to all content ⋅ pick a username

linwanrun1357 If we assume that they are not carriers (in the recessive case) Then how came it can be AR？！！ +3

catscan1979 ^exactly what's said above here. I think x-linked recessive is the least likely, but not impossible. +4

furkan7 How is x linked recessive is the least likely when we need 2 carrier females for compatibility of both autosomal recessive and X linked recessive inheritence to this pedigree? I think probability of these two are the same. Am I missing something? +1

You must be logged in to vote!
You must be logged in to vote!

+2 upvote downvote
submitted by ayhamai(2)

get full access to all content ⋅ pick a username

x-linked is not possible if the woman was not a carrier autosomal recessive is not possible if the woman was not a carrier so, why we choose x-linked

get full access to all content ⋅ pick a username

utap2001 In all pedigree questions, you check up for 3 things: 1. if the inheritance is continuous(not skip generation), if yes-> dominant; no-> recessive. 2. check male to son transmisstion, if yes-> autosominal; no-> X-linked. 3. check male to daughter transmisstion, if no-> mitochondrial. https://step1.medbullets.com/biochemistry/102036/modes-of-inheritance +2

You must be logged in to vote!
You must be logged in to vote!

+1 upvote downvote
submitted by ∗therealslimshady(42)

get full access to all content ⋅ pick a username

I thought there weren't supposed to be trick questions on these things.

get full access to all content ⋅ pick a username

agraham416 Yeah I misread the question too. +1

You must be logged in to vote!
You must be logged in to vote!

+0 upvote downvote
submitted by ∗freemanpeng(7)

get full access to all content ⋅ pick a username

No one talks about AR? That's much more unlikely in this case than XR

get full access to all content ⋅ pick a username

You must be logged in to vote!
You must be logged in to vote!

+0 upvote downvote
submitted by ∗j44n(141)

get full access to all content ⋅ pick a username

I got thrown off because there's an arrow point to the three unaffected daughters (with an affected father) so I thought XLR because they'd be carriers. And there was no generation skipping so that made me think AR

get full access to all content ⋅ pick a username

You must be logged in to vote!
You must be logged in to vote!

+0 upvote downvote
submitted by failingnbme(3)

get full access to all content ⋅ pick a username

This is the 3rd question I didn't read properly fk fk fkityfk

get full access to all content ⋅ pick a username

You must be logged in to vote!
You must be logged in to vote!

Must-See Comments from nbme24

seagull on Intestinal mucosa
tissue creep on Ask the roommate not to smoke in the apartment
drdoom on Adenosine
seagull on Increased serum testosterone concentration
atstillisafraud on Lamins
niboonsh on Only cookies are independently associated ...
atstillisafraud on Scar formation
lamhtu on Decreased adherence
drachenx on Damage to the rectovaginal septum
drdoom on Intestinal mucosa
azibird on Coronavirus
lsmarshall on Organic acid metabolism disorder
sympathetikey on Inhalant abuse
tea-cats-biscuits on Eosinophils