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Understanding the Y-DNA STR Testing Process
Category: Y-DNA » Y-DNA STR

Once your buccal swabs arrive in the testing laboratory, the following steps are involved to obtain your Y-DNA haplotype:

1. When the laboratory receives the cheek swab samples, the cells are removed from the swab into an eppendorf tube.

2. The cells are then lysed (broken apart) to release the DNA.

3. The DNA is purified and quantitated.

4. The STR markers on the DNA are amplified using a process known as polymerase chain reaction (PCR). During PCR, the specific regions of the DNA to be analyzed are amplified so that they can be analyzed. A primer pair is used to amplify each marker.

5. The DNA strand is heated to separate the strands and the primers anneal onto the DNA template. TAQ polymerase amplifies the region between the primers. The primers are designed to surround the STR marker. Using a series of heating and cooling steps, the DNA is repeatedly amplified using this technique. In a matter of an hour, millions of copies of the Y-STR markers are produced from a single original DNA strand. Each specific primer pair is labelled with a colored dye. Thus, all of the PCR products have a color coded label attached.

6. The DNA fragments produced by the PCR reaction are examined using a laser (capillary laser sequencing). During sequencing, an electrical current is used to force the DNA fragments to pass through a gel matrix within a fine capillary tube into a laser beam. As the DNA passes across the laser beam, the laser beam records the type of dye associated with the fragment, and the size of the fragment is recorded (smaller fragments pass more quickly through the gel and larger fragments pass through more slowly).

7. The results of the analyses appear as peaks on a computer output and these peaks each correspond to a Y-Chromosome marker. Based on the position of the peaks, the laboratory will be able to determine the exact number of repeats in the DNA marker and thus obtain the exact haplotype of that individual’s DNA.

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