dideoxy DNA sequencing
Replication
of the DNA strand in a sequencing
reaction begins with (A) a set of primed
template ssDNA molecules, and all four dNTPs
plus one (B) ddNTP,
in the example ddATP.
The -H on the 3'-C prevents further
extension. (C) The region to be sequenced
includes three T positions. The ddATP is randomly
incoporated during strand synthesis, such that chain
growth terminates at each T where a
complementary ddA
has been incorporated. Four separate
reactions with each of the four ddNTPs produces
a complete set of fragments that differ by plus or
minus one nucleotide over the entire length of the
template DNA..
Figure © 2012 TA Brown, Introduction
to Genetics (1st ed.); additional
text © 2012 by Steven M. Carr