Technical considerations


After DNA typing a two step process is used to determine whether two samples arose from a single source. Firstly, DNA-banding patterns are compared visually. If these banding patterns do not match, then an exclusion is declared and no further analysis is required. Secondly a visualized match is verified by a technique known as computer-assisted allele sizing. The calculated sizes of an apparent match should fall within 2.5% of each other, if they do not the samples should be considered as non-matching. If the DNA-banding pattern of a sample cannot positively be determined, the results should be considered inconclusive.


Except for identical twins, no two persons should have an identical DNA sequence. Unique identification with DNA typing may be achieved if enough sites of variation are examined. Although present DNA typing systems analyze few variation areas, a match between two DNA patterns provides strong evidence that they originated from the same source. The interpretation of DNA typing requires a reliable and reproducible method which estimates whether a random sample from a person matches by chance a forensic sample at sites of DNA variation.


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