Answer:
The addition of different-colored fluorescent tags on each dideoxynucleotide (ddNTP) improved the Sanger DNA sequencing method by allowing for multiple DNA fragments to be sequenced in a single reaction and detected simultaneously.
In traditional Sanger sequencing, DNA fragments are separated by electrophoresis on a denaturing polyacrylamide gel, and the identity of the terminating nucleotide at each position along the DNA sequence is determined by autoradiography or fluorescent detection. In contrast, fluorescent Sanger sequencing uses fluorescently-labeled ddNTPs, each labeled with a different color, to terminate DNA synthesis. The fragments are then separated by capillary electrophoresis, and the sequence is read by detecting the color of the fluorescent tag at each position.
The use of different-colored fluorescent tags allowed for multiple DNA fragments to be sequenced in a single reaction, as each ddNTP could be labeled with a different color. This greatly increased the efficiency of the sequencing process and allowed for the rapid, high-throughput sequencing of DNA. Additionally, the use of fluorescent tags eliminated the need for radioactive labeling and autoradiography, which was a significant advance in terms of safety and convenience.
In summary, the addition of different-colored fluorescent tags on each ddNTP improved the Sanger DNA sequencing method by allowing for high-throughput sequencing of DNA and eliminating the need for radioactive labeling and autoradiography.