Question

During DNA sequencing, why is the autoradiogram read from bottom to top to arrive at the original sequence ?

Hint:

Remember how DNA fragments are separated on the basis of size and the different properties of the vectors.

Answer 1

(i) Autoradiogram Reading Direction: Autoradiograms in DNA sequencing are read from bottom to top. Smaller DNA fragments, having migrated fastest to the gel's bottom, are identified first. Larger fragments remain at the top. Since DNA synthesis proceeds in a 5' to 3' direction, reading from bottom to top reveals the sequence in this orientation. (ii) Advantages of Single-Tube DNA Sequencing: Single-tube DNA sequencing is preferred for its improved safety and efficiency. It is automated, expedites the sequencing process, and utilizes a single electrophoresis lane for simplification. The use of fluorescent dyes enhances safety over traditional radioactive isotopes. Results are directly viewable and storable on computers. (iii) M13 Vector for Single-Stranded DNA: The M13-based vector is the optimal choice for sequencing single-stranded DNA. Its capacity to carry single-stranded DNA within viral particles makes it suitable for single-stranded DNA cloning.