Topscore Exam #3 Question #34

[jdpaul14]

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Ok, so this is a weird question so whoever can answer this, well I give you mad props!

Q: A woman carries a sex-linked lethal gene that causes spontaneous abortions. She has 6 children, how many of the six would you expect to be boys?

A: 2


How the heezy did they get this answer??

 

[bbwreckerz04]

She has 6 children so you know that they aren't aborted. 1/3 of 6 is 2.

How you get 1/3 is that the affected is XY is automatically aborted so it can not be part of the 6 children she has. When you do the punnet square you should you get that 50% of boys abort, so that leaves 1/3 boy for every 2/3 girl so 1/3 for every birth that it is a boy. I'll explain more if you get confused.

 

[jdpaul14]

I'm with you up until 50% of the boys are aborted...but how did you get 1/3? I'm still confused on that part, thanks for helping by the way 🙂

 

[jdpaul14]

OHHHHH...ok I get it now!...so your saying that once we do the punnet square and figure 50% of the boys will be aborted, we in essence know that only 3/4 of the children she has the possibility of conceiving will not be aborted. Out of these 3 children, 1 of the 3 will be a boy...so (1/3)*(6) = 2

Thanks a lot buddy!

 

[iwannabadentist]

X(L)-Y will die with the lethal copy of the X chromosome. X(L) is lethal so only 1 out of 2 boys and 3 out of 4 children will survive. Out of the 3 children that survive, only 1 will be a boy. 1/3 probability of a living boy to be born so 2/6 children will be boys. 👍

 

[jdpaul14]

Appreciate ya!!! 🙂

 

[bbwreckerz04]

OHHHHH...ok I get it now!...so your saying that once we do the punnet square and figure 50% of the boys will be aborted, we in essence know that only 3/4 of the children she has the possibility of conceiving will not be aborted. Out of these 3 children, 1 of the 3 will be a boy...so (1/3)*(6) = 2

Thanks a lot buddy!

Yea just like that you really don't need to do a punnet square to figure it out, I put it there as an example so you can see it better.

 

[Shinpe]

Hmm question

Would it look like something like this:

--| X(L) | X
X | X(L)X |XX
Y | X(L)Y |XY

So wouldn't both one boy and one girl die? and only the two on the right survive? Or I'm missing sth really basic? So shouldn't 50% of the ones surviving be dudes??

 

[iwannabadentist]

Hmm question

Would it look like something like this:

--| X(L) | X
X | X(L)X |XX
Y | X(L)Y |XY

So wouldn't both one boy and one girl die? and only the two on the right survive? Or I'm missing sth really basic? So shouldn't 50% of the ones surviving be dudes??

the girl wouldnt die because she would still have one copy of the good chromosome from the father. the boy only has one bad copy from the mother so he dies.

 

[bbwreckerz04]

Hmm question

Would it look like something like this:

--| X(L) | X
X | X(L)X |XX
Y | X(L)Y |XY

So wouldn't both one boy and one girl die? and only the two on the right survive? Or I'm missing sth really basic? So shouldn't 50% of the ones surviving be dudes??

She's a carrier of XLR gene otherwise I assume she would of been aborted herself, so in female it requires 2 lethal gene to abort.

 

[Shinpe]

the girl wouldnt die because she would still have one copy of the good chromosome from the father. The boy only has one bad copy from the mother so he dies.

nvm

 

[Shinpe]

She's a carrier of XLR gene otherwise I assume she would of been aborted herself, so in female it requires 2 lethal gene to abort.

Ok nevermind, that completely makes sense now. Thanks