U.S. flag

An official website of the United States government, Department of Justice.

Assigning forensic body fluids to donors in mixed body fluids by targeted RNA/DNA deep sequencing of coding region SNPs

NCJ Number
Date Published
13 pages

This article reports on a study whose results indicate that associating donors and body fluids by means of comparing mixture ratios in RNA and DNA is not recommended, and it introduces a set of 35 coding region SNPs (cSNPs) in body fluid-specific mRNA transcripts that represent a direct link between the body fluids and their donors.


Biological traces found at crime scenes are analyzed not only to genetically identify the donor(s) but also to determine the composition of the stain. For some cases, it is essential to associate a body fluid with a donor. Especially in mixed body fluid stains, but also in body fluid stains that appear to be single-source, this may be important. Linking a DNA profile (sub-source level) with evidence from a presumptive test or mRNA analysis (source level) is not straightforward. In the current project, the discrimination power of the cSNPs was estimated based on allele frequencies calculated from a population sample (n = 188), and researchers investigated the practical application of the cSNPs in different scenarios. The results demonstrate that more cSNPs are needed to improve the discrimination power; however, the findings are, since the study was able to associate donors with body fluids in mixtures of different body fluids, as well as in stains where both donors had contributed the same body fluid, e.g. a blood-blood mixture. In addition, the cSNP assay can be used for body-fluid identification. The results of this proof-of-concept study support the use of cSNPs to assign body fluids to the respective donors. (publisher abstract modified)

Date Published: January 1, 2020