Question

A researcher has identified the location of the gene in a eukaryotic cell that codes for protein P and has managed to excise it from the DNA. She has also generated DNA from the mRNA that codes for the protein. If she runs these two sequences through gel electrophoresis, what should she expect to see?
It must be noted that the wells where the DNA was loaded onto the gel are at the top of the gels shown below.

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

Excised DNA would be the original sequence. The cDNA is synthesised from mRNA (after post-transcriptional change), hence does not contain introns like the unprocessed excised sequence.
Gel electrophoresis separates fragments based on size. Molecular size of excised DNA will be greater than cDNA. Hence, the former will move slower as compared to later one. Thus, option c is the most appropriate one.