Plzzz explain me this bio stuff...

[hopelessdoc]

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A woman carries a sex-linked lethal gene that causes spontaneous abortions. She has 6 children. How many of her children would you expect to be boys?
A) None
B) 1
C) 2
D) 3
E) 4

thanxxx...

 

[RozhonDDS]

I'd say D (3), mainly because I dont think her being a carrier has any effect on the sex of her children. With this being said if it did have an effect on the sex it would effect the women until they were going to give birth, and 50% of 6 is 3, so i'd say 3 but it's just a guess.

 

[armorshell]

The answer is 2.

If you write out the Punnet square, 50% of her male children will be aborted. Because she has 6 children, we know that the ratio of boys to girls will be 1:2 instead of 2:2 because of the mutation.

Therefore, she will have (on average) 4 girls and 2 boys.

 

[tinman831]

The answer is 2.

If you write out the Punnet square, 50% of her male children will be aborted. Because she has 6 children, we know that the ratio of boys to girls will be 1:2 instead of 2:2 because of the mutation.

Therefore, she will have (on average) 4 girls and 2 boys.

Yep. The answer is two.

mother = xix where i is the lethal gene on the x
father = xy

xix cross xy =
xix
xiy (this one will be aborted)
xx
xy

So in 3 children, 2 will be female and 1 will be male. Out of 6 children, 4 will be female and 2 will be male.

 

[FatalExtraction]

yup its 2... if u draw out a punnet square in your head ull notice since the mother isnt dead from this...she must be a carrier which means its recessive...us males have it bad when their only X chromosome are defective so one of the guys will die...you can think of it as if she has 2 punnet squares worth of kids (because you need at least six kids)...if she has that many kids two of them wil be spontaneously aborted..so 4 boys - 2 aborted gives you 2 boys left...such a sad question no?

hoped that helped if not then listen to armorshell or tinman...good luck on ur dat's guys

 

[JohnDoeDDS]

Im ghaving trouble understanding that one punnet square equals 3 kids. Could someone explain?

 

[FatalExtraction]

hey while im up i might as well try to help...

so the trait the mother has has to be recessive -> meaning shes Heterozygous for it and thus, a carrier

draw out a punnet square with XD Xd (cross) XD Y

(the d is for death and D is normal)

you'll see that whoever gets the recessive trait for death will not be alive and the only one that gets it is one of the guys ---> so 3 of the 4 kids survive, 1/2 of the boys survive. She needs 6 kids total which means you need at least another punnet square. same thing happens again and now out of all of your kids (which at this time is 6 because 2 boys have died) this leaves only 2 boys alive with the others being girls

hope that helps...if not ill shut up now...have a nice day