Principles of Forensic DNA
for Officers of the Court
Principles of Forensic DNA for Officers of the Court
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Module 7 :: Statistics

Topic 4 :: Interpreting Mixtures

Calculation of Random Match Probability for Mixed Samples

Random match probability can be calculated in mixtures that involve two contributors and one contributor is known. For example, in sexual assault cases a vaginal swab is analyzed for the presence of semen and a DNA profile is developed from the sperm fraction and non-sperm fractions.

In some cases, as mentioned above, the sperm fraction results in a mixed sample that is consistent with the victim and the sperm donor. If the mixture reveals four alleles14, 15, 16, and 17and the victim is known to contribute the 14 and 15 alleles, it can be inferred that the sperm donor must be responsible for the 16 and 17 alleles.

Continued

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