The DNA tests are done for what are known as "Short Tandem Repeats". These are spots in the DNA where the same sequence (2-6 base pairs) is repeated several ti

The DNA tests are done for what are known as "Short Tandem Repeats". These are spots in the DNA where the same sequence (2-6 base pairs) is repeated several times. Unrelated people have different numbers of repeats. They're looking at a dozen or more locations. The number of repeats at any location is unrelated to the number of repeats at another location. So, if you've got a number between 2 and 10 or 20, you've got 10% to 5% of the population that has that particular number of repeats. 1/(0.1 ^ 13) is 10 trillion which is the ballpark for the number of variations for STRs possible on a 13 location test. The data that is stored looks like [6 4 12 16 2 15 19 18 14 5 3 7 8] https://en.wikipedia.org/wiki/Microsatellite https://en.wikipedia.org/wiki/Microsatellite https://en.wikipedia.org/wiki/STR_analysis https://en.wikipedia.org/wiki/STR_analysis