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STR Data Analysis and Interpretation for Forensic Analysts

Mixtures with Known Contributor(s)

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It is common to obtain samples where one of the contributors (e.g., the victim) is known. In these cases, it may be possible to infer an unknown profile by subtracting the contribution of the known donor from the mixed profile.01

In general, this approach is taken on intimate samples such as vaginal swabs, fingernails, breast swabs, neck swabs, and clothing items removed from a person's body in situations where it is likely that there are no more than two contributors. It may be possible to infer unknown profiles from mixtures with more than two contributors, but that would be considerably more complex.

An analyst can use percent mixture contribution and peak height percentages to aid in inferring profiles from mixtures with known contributors.

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