The image below shows a Sanger DNA sequencing gel where one ingredient was left out of all sequencing reactions. The top of the gel is the anode and the bottom of the gel is the cathode. The gel was turned on and ran correctly. What is the MOST likely missing ingredient?
A) dNTPs
B) ddNTPs
C) radioactive DNA primer
D) DNA polymerase
E) template DNA

Question

The image below shows a Sanger DNA sequencing gel where one ingredient was left out of all sequencing reactions. The top of the gel is the anode and the bottom of the gel is the cathode. The gel was turned on and ran correctly. What is the MOST likely missing ingredient? 
A) dNTPs 
B) ddNTPs 
C) radioactive DNA primer 
D) DNA polymerase 
E) template DNA

Quizplus · Accepted Answer

The ladder pattern on the gel indicates that DNA fragments of different lengths were generated, suggesting that some form of termination was occurring during the sequencing reaction. In Sanger sequencing, termination occurs when a ddNTP is incorporated in place of a dNTP, resulting in chain termination and the production of a fragment of a specific length. If ddNTPs were not added to the reaction, termination would not occur and the DNA fragments would continue to elongate, resulting in a smear rather than distinct bands. Therefore, the most likely missing ingredient is ddNTPs.

The Image Below Shows a Sanger DNA Sequencing Gel Where