Zygote chromosomes question (kaplan)

[Spectar]

Question with answer
A zygote destined to be female will have two X chromosomes. Which of the following statements is true regarding the genetic makeup of those two X-chromosomes, assuming that no random mutation has occurred?

She will have an X-chromosome that is exactly identical to that of her maternal grandmother.

She will have an X-chromosome that is exactly identical to that of her paternal grandmother.*

She will have an X-chromosome that is exactly identical to her mother.

She will have an X-chromosome that is exactly identical to her maternal grandfather.

Explanation:
If there are two of one kind of chromosome, those chromosomes will be subject to crossing over during prophase I. Thus, any X-chromosome contributed by the mother of the child will have undergone crossing over. Thus, the child will not receive chromosomes that are exactly identical to those of her maternal grandmother, maternal grandfather, or mother. On the other hand, the X chromosome contributed by her father will not have undergone crossing over. Thus, she will have the same X-chromosome as her maternal grandmother. Choice (B) is correct.


My question: Using the same logic they provided, how could one of the X chromosome given by the dad be exactly the same as the paternal grandmother, if her X chromosomes can cross over just like the child's mother? Shouldn't the answer be "It's not possible to have an X chromosome exactly identical to anyone because crossing over can happen from any mother"

Thanks

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[Ascleoius]

I think the answer should be "she will have an X-chromosome that is exactly identical to her father because crossing over can happen from any mother."

 

[Pono_0001]

ya just keep in mind that kaplan and all the other prep book are not real mcat, even TBR has mistakes like these. Keep in mind while cross over in non psuedoautosomal region, such as SRY, can lead to defects, cross-over does happen in pseudoautosomal region of X and Y, in fact failure in crossover between X and Y can lead to male infertility (see the link below). but it's hard to know what's right and wrong in these tests. It can be right or wrong depending on how wrong the other choices are. So for this question you can kinda deduce B to be the Least Wrong answer. But I wouldn't obsess over this question as it's clearly a badly designed question that I doubt you'll see on the MCAT A better choice would be She will have an X-chromosome that is exactly identical to that found in one of her paternal grandmother's egg.

 

[Ascleoius]

ya just keep in mind that kaplan and all the other prep book are not real mcat, even TBR has mistakes like these. Keep in mind while cross over in non psuedoautosomal region, such as SRY, can lead to defects, cross-over does happen in pseudoautosomal region of X and Y, in fact failure in crossover between X and Y can lead to male infertility (see the link below). but it's hard to know what's right and wrong in these tests. It can be right or wrong depending on how wrong the other choices are. So for this question you can kinda deduce B to be the Least Wrong answer. But I wouldn't obsess over this question as it's clearly a badly designed question that I doubt you'll see on the MCAT A better choice would be She will have an X-chromosome that is exactly identical to that found in one of her paternal grandmother's egg.

hi I couldn't see the link?

 

[Spectar]

Thank you for the clarification. Just wanted to make sure I wasn't the only one