Forensic Dentistry, Second Edition

dna and dna evidence 131

extension. At the end of each cycle the quantity of DNA template has
been doubled.
Polymerase and Ta q: Polymerase is the enzyme that adds nucleotides to
the new strand of DNA during PCR. The step is call extension.
Since the high temperature in the denaturing step of PCR deacti-
vates most polymerases, the isolation of a thermostable polymerase
from the thermophilic bacterium Thermus aquaticus (Ta q) allowed
multiple cycles of denaturing and annealing to occur without loss
of enzyme activity.
Primer: A small segment of complementary DNA that establishes the
starting point for DNA synthesis in PCR is called an oligonucleo-
tide primer. It signals the point at which polymerase begins to add
nucleotides.
Sequencing: Current forensic mtDNA sequencing is based on modifications
of the Sanger chain termination method that allows the scientist to
determine the order of the nucleotide bases—adenine (A), guanine
(G), cytosine (C), thymine (T)—in a given segment of DNA.
Short tandem repeat (STR): These are defined as two or more nucleotides
in a fixed sequence and repeated in a continuous series. For example,
i f t h e t e t r a nu c l e o t i d e (f o u r-nu c l e o t i d e) s e q u e n c e [A- G -T-A] i s r e p e a t e d
nine times on one chromosome at a specific locus and eleven times
at the same locus on the homologous chromosome, the STR profile
for that individual can be said to be 9,11 at that locus. Most forensic
analytical procedures will target six to seventeen loci on autoDNA
and Y-DNA for STR profiling.

Acknowledgments

The authors gratefully acknowledge the support of Dr. Kevin Torsky at the

Joint POW-MIA Accounting Command Central Identification Laboratory

(JPAC CIL) and LTC Louis N. Finelli of the Armed Forces DNA Identification

Laboratory (AFDIL) for their assistance.

References

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3. Farley MA, Harrington JJ, eds. 1991. Forensic DNA technology. Chelsea, MI:
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