Gel images from an automated DNA sequencer
From the original
DNA template, the sequencing reaction synthesizes a new DNA
strand that incorporates a set of fluorescently-labeled ddNTPs
into the DNA (centre). The newly synthesized DNA
is separated by size in an electrophoretic field, and the
fluorescence colours are activated by a scanning laser, tracked,
and read by a photometer. The gel image (left) is a "false colour"
representation of 24 different DNA sequences, each lane
from a separate sequencing reaction; automatic tracking for one
lane is shown by the white trace. In the magnified view
(right), the sequencing ladder in each lane has four
different coloured bands that correspond to each of four DNA
bases: A C
G & T. Each channel is
converted to an individual chromatogram
for that DNA sequence; the order of coloured peaks is
converted to a DNA sequence.
For example, the first few bases of the fourth lane will be read
. [Click here for an animation].
HOMEWORK: Popular accounts (like "Jurassic Park") suggest that "DNA sequences are read by a laser'" Explain why this is incorrect.