A question on genetics...

[whawha]

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A woman carris a sex-linked lethal gene that causes spontaneous abortion. She has six children. How many of her children would you expect to be boys?

I CANNOT figure this out for some reason....frustrating...

Edit: Answer is TWO...

Thanks in advance.

 

[UCB05]

A woman carris a sex-linked lethal gene that causes spontaneous abortion. She has six children. How many of her children would you expect to be boys?

I CANNOT figure this out for some reason....frustrating...

Sex-linked lethal carrier implies that the woman is heterozygous for the gene, X*X. All males are hemizygous for X, so her husband has to be normal XY. The offspring of the two will have the genotypes:

XX = normal female
X*X = carrier female
XY = normal male
X*Y = lethal male, spontaneously aborted

Since the X*Y pregnancy never goes to term, that leaves a 1 girl : 1 girl : boy birth ratio. 1/3 should be boys. Out of 6 children, that means 2 boys.

 

[whawha]

Sex-linked lethal carrier implies that the woman is heterozygous for the gene, X*X. All males are hemizygous for X, so her husband has to be normal XY. The offspring of the two will have the genotypes:

XX = normal female
X*X = carrier female
XY = normal male
X*Y = lethal male, spontaneously aborted

Since the X*Y pregnancy never goes to term, that leaves a 1 girl : 1 girl : boy birth ratio. 1/3 should be boys. Out of 6 children, that means 2 boys.

Thank you 👍