Gene sizes and vectors

[mmcoffee]

This is the second time I've come across something like this. How big, is too big? (referring to choice c and d explanation)

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[RH8448]

I remember doing this question. The size of genes of course varies widely. From what I remember it was a loss of function so the gene itself was still present. The point of this question is not about the size of the gene but rather that a promoter is necessary for the expression of a gene.

Because 79 exons are present, this implies that the gene is used for many many different kinds of proteins. The gene is spliced in 78 different ways for that one protein. So, it is a large gene. I forgot exactly how the loss of function occurred. But, like I said I believe the focus of this question it to recognize that the promoter is what is important to induce transcription, if the gene is already present but not expressed.

 

[Altius Premier Tutor]

Someone who works in a genetics lab might have a general sense about "You can get a 5kb sequence integrated successfully using x vector, but a 10kb gets sketchy..." but that kind of specific knowledge is well beyond the MCAT. I would not try to memorize some rule of thumb about "size limit" in terms of base pairs, kDa, exons, etc. This is probably just an artifact of the person who authored the question using a justification for excluding those distractors that is slightly outside of the AAMC boundaries for expected knowledge. I didn't read the passage, but it appears to me that C and D are simply unnecessary--to deliver the entire gene to the entire body vs. muscles only, if it is the AOS sequence which the passage indicates is the necessary missing piece. That logic, generally speaking, is MCAT-like logic. Distractors may offer experimental designs or procedures which go too far, or unnecessary, while a more specific and limited approach addressing the precise problem will be the correct answer. Hope that helps!