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Two DNA tests help criminalists identify people

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Posted: Sunday, March 18, 2012 1:19 am | Updated: 12:02 pm, Sun Mar 18, 2012.

Two tests are used to help identify individuals through DNA analysis, according to John Tonkyn, criminalist supervisor with the Department of Justice’s lab in Richmond, Calif.

The first test criminalists used is a test all DNA labs across the country conduct.

Initially, criminalists use a chemical known as Ethylenediaminetetraacetate to “purify” the DNA sample. The drug separates things like proteins and fats that maintain the structure of the cell’s walls, which protect the DNA within the nucleus of the cell.

Ethylenediaminetetraacetate (EDTA) weakens the cell to the point that the walls collapse or tear, releasing the cell’s contents and DNA for analysis.

Also, EDTA protects and preserves the integrity of DNA by inhibiting enzymes that are normally present in the cell, which can fragment the DNA and render it unusable.

Once the DNA is all by itself, criminalists have a set of 16 genetic markers that can test for things such as gender and other properties only inherited — or found — in blood relatives.

“This is our best DNA profile,” Tonkyn said of the analysis once the test is complete. “This test provides us with the best identification for individuals because it give the most unique DNA profile.”

But, if there is not enough DNA extracted from the freezer mill or the thermal cycler, Tonkyn said criminalists can use a second test — the mitochondrial DNA test.

Mitochondria is part of the cell structure which also contains DNA, but the issue with the test is that the DNA comes only from the mother. That DNA is also shared with other relatives of the mother, making the sample less unique.

Contact reporter Katie Nelson at katien@lodinews.com.

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