Biology Reference
In-Depth Information
dideoxynucleotides in four separate sequencing reactions leads to termination of chain elongation
leading to DNA strands of varying lengths. These are separated by denaturing polyacrylamide
urea gels with each of the four reactions run in one of the four individual lanes (lanes A, T, G, C).
Visualization of the DNA bands either by autoradiography or ultraviolet light facilitates reading of
DNA sequence from the X-ray fi lm or gel image. The relative positions of the different bands among
the four lanes are then used to infer the DNA sequence (from bottom to top). These methods are
suitable to sequence relatively short fragments of DNA ~300 to 1000 nucleotides long. Out of a number
of modifi ed Sanger methods, fl uorescent labelling of primers at 5'-end and the dideoxynucleotides
has gained popularity and facilitated the development of automated and high-throughput DNA
sequence analyzers. Vast majority of the sequencing projects employ this method. Chain-termination-
based commercial kits are now available. Figure 2 elaborates the organism-based sequencing and
Figure 2:
Schematic representation of steps involved in genomics and metagenomics, transcriptomics and proteomics.
