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New article next to Short Tandem Repeat (STR) analysis New article below Short Tandem Repeat (STR) analysis

One of the most common ways of obtaining aDNA profileis to perform a Short Tandem Repeat (STR) analysis. The procedure is as follows:

  • 1)Extract and purify the DNAfrom a sample.

  • 2) Use thePCR techniqueto amplify the Short Tandem Repeats (STRs). A set ofprimersplaced on the flanking regions of a variable sequence will amplify fragments of different lengths depending on the number of repeats (see image below). There is a chance that two individuals will share the same number of repeats at a certain repeated site. If we were to use only one primer set (amplify only one repeated region), the risk that an individual shares the same number of repeats with another one would be too great. Therefore, a minimum of 13 tandem repeat sites are investigated while performing DNA profiling.

  • 3) Usegel electrophoresisto analyze the length of the tandem repeats and obtain the DNA profile.

Potential short tandem repeat units and targeted region fragment lengths. Strands of DNA with varying numbers of repeat units are shown. In each strand, a primer is located at the start and end of the tandem repeat units, so that the amplified fragment will differ in size depending on the number of times the unit is repeated. In the example, 5 different fragment lengths are shown, corresponding to a different number of tandem repeat units, from 7 to 11 units. The repeat units can consist of different numbers of nucleotides. For example, a 2 nucleotide repeat unit could consist of C.A. repeated consecutively. The number of repeated units will determine the fragment size, and it can vary between individuals. Repeat units can also consist of 3, 4, or even 5 nucleotides.

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