A piece of DNA has been sequenced by automated dideoxy sequencing, in which each dideoxyribonucleoside triphosphate was labeled with a fluorescent tag of a different color. The data corresponding to a small segment with the sequence 5′-TGCCACA-3′ is shown in the following diagram. Knowing that ddGTP has been labeled with green fluorescence, what color do you think was the fluorescent tag used to label ddTTP in the sequencing experiment?
A) Blue
B) Green
C) Red
D) Yellow

Question

A piece of DNA has been sequenced by automated dideoxy sequencing, in which each dideoxyribonucleoside triphosphate was labeled with a fluorescent tag of a different color. The data corresponding to a small segment with the sequence 5′-TGCCACA-3′ is shown in the following diagram. Knowing that ddGTP has been labeled with green fluorescence, what color do you think was the fluorescent tag used to label ddTTP in the sequencing experiment? 
A) Blue 
B) Green 
C) Red 
D) Yellow

Quizplus · Accepted Answer

The labeled ddTTP (red) is incorporated twice, opposite to the A nucleotides in the sequence.

A Piece of DNA Has Been Sequenced by Automated Dideoxy