D) To read the DNA sequence of the synthesized strand in the 5'-to-3' direction, the gel is read from top to bottom.
Explanation:
The DNA sequence of the synthesized strand in the 5'-to-3' direction is read from the bottom to the top. On the electrophoresis gel, bands corresponding to the smallest DNA fragment migrate to the bottom of the gel. Meaning, the DNA primer fragment would be at the bottom and immediately above it would be the fragment that had fewer dNTPs (deoxynucleotidetriphosphates) incorporated prior elongation termination by an incorporated ddNTP.
