Biology Reference
In-Depth Information
Figure 7.4
Autoradiograph of a sequencing gel obtained by the dideoxy chain-termination method. Four
different reactions are carried out in which DNA synthesis of a complementary DNA chain is terminated
by incorporating a radiolabeled dideoxy base (ddATP, ddCTP, ddGTP, or ddTTP) rather than a deoxy
base (dATP, dCTP, dGTP, dTTP). The resulting fragments of synthesized DNA are visualized by acryl-
amide gel electrophoresis and autoradiography. The sequence is read by determining which lane contains
each succeeding DNA segment, as determined by a band. Thus, reading
from the bottom
, the shortest frag-
ment has a band in the T lane (just above the line). The next band is a C, then the next is an A, and so
on. Bands at the very top and bottom of the gel are not read. This sequence is a portion of the
mariner
transposable element cloned from the predatory mite
Metaseiulus occidentalis
(
Jeyaprakash and Hoy 1995
).
