Hi,

This question has also come up in the biochemistry section, so I will quote the answer given here:

Hi,

This is a bit of a tough question.

You have been given only the RNA of the TP53 gene as stated in the question stem(here the implication is mRNA). This mRNA has been spliced at this point, removing introns and promotor sequences starting transciption.

To do this Duplex PCR sequencing technique , you need to have double stranded DNA, so you would have to get your DNA from the reverse transcription of the mRNA provided.

Because exons 3 and 5 are expressed in the mRNA, it is likely that mutations in both can be easily detected in Duplex PCR, eliminating B and C. Similarly, the DNA you get from reverse transcription also has an untranslated region, meaning D is unlikely as well.

However, the AT regions of DNA upstream of the promoter usually refer to a TATA box, which is part of the promoter region that is spliced out of mRNA - because our source of information is mRNA, we would not be able to see this region and therefore cannot comment on its variation, suggesting that A is the correct answer.

You don't have to fully understand the sequencing library (essentially it is rejustifying that the only information you have is the RNA sequence in this question), the question is more probing what gets spliced out in mRNA splicing.

Sometimes the EK answer explanations give more advanced information than needed.

Please let me know if this is unclear.