A gel electrophoresis migration pattern displaying polymerase chain reaction (PCR) products shows four strong bands. The lengths of the four pieces of DNA are approximately in the ratio of 1:2:3:4. The longest band is cut out of the gel, and PCR is repeated with the same primers. Again, a ladder of the same four bands appears in the gel. What does this result reveal about the structure of the encoded protein?A) The protein is a tetramer of a single peptide. B) Up to four copies of the DNA ligate to form circular DNA molecules. C) Four copies of the protein‑coding gene occur in the genome. D) The encoded protein contains four repeats of a specific sequence. E) Portions of the protein are encoded by four different genes.

D) The encoded protein contains four repeats of a specific sequence.

Explanation:

The polymerase chain reaction is a technique used to replicate or amplify the amount of DNA sample.

The technique employs running the DNA samples on the gel through which the DNA samples run based on their sizes.

The large-sized DNA fragment runs to a less distance whereas the small-sized DNA run to a large distance.

In the given question, four sizes of DNA bands are formed in the ratio of  1:2:3:4 which shows that the proteins encoded by this DNA have four repeats of a specific sequence of the template strand. This was confirmed when the largest band sample was again used as a sample of PCR and the PCR resulted in the four bands in similar  1:2:3:4.  

Thus, Option-D is the correct answer.

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