TS#3 Genetics

[thakdha]

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A woman carries a sex-linked lethal gene that causes spontaneous abortions. She has six children. How many of her children would you expect to be boys?
A. None
B. One
C. two
D. three
E. Four


I thought the answer was 3 since its always a 50% chance of having a boy every time. So, out of 6 children 3 are boys. The answer is C

 

[thakdha]

Can anyone please answer this question for me?

 

[bpenly]

In the cross you have:

X^L X^L = Normal Female

X^L X^l = Heterozygote carrier of lethal allele (female)

X^L Y = Normal Male

X^l Y = Affected Male - Aborted. This leaves 1/3 of all possible children to be a boy. Multiply by two to get the answer to get the answer of two.

 

[thakdha]

thanks

 

[bpenly]

No problem. I hope my explanation and punnett square made sense. Good luck on the DAT.