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Figure 7 of Mitochondrial DNA Analysis at the FBI Laboratory by Isenberg and Moore (Forensic Science Communications, July 1999)

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July 1999   Volume 1   Number 2

Mitochondrial DNA Analysis
at the FBI Laboratory

Figure 7
Cycle Sequencing

Figure 7: Cycle Sequencing

The cycle sequencing process is very similar to the polymerase chain reaction, but the reaction is terminated by the incorporation of dideoxynucleotide triphosphates (ddNTPs) before the DNA strands can extend to their full length. Fluorescently labeled ddNTPs are mixed with regular dNTPs, a primer, and the DNA template for the reaction. During the course of the reaction, the ddNTPs compete with the dNTPs for positions on the DNA template, resulting in a pooled set of fragments differing by a single base in length. At the end of each strand is a fluorescent dye molecule, the color of which depends on the base at the terminal position of the strand. The different dye colors identify the base present at the end of each strand, thus providing a method for determining the sequence of the entire strand.

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FORENSIC SCIENCE COMMUNICATIONS     JULY 1999   VOLUME 1   NUMBER 2

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