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Modeling Forward Stutter: Toward Increased Objectivity in Forensic DNA Interpretation

NCJ Number
Date Published
November 2014
6 pages
This study investigated possible explanatory variables for the occurrence and size of forward stutter for four different autosomal multiplexes, as well as models used to predict the expected heights of forward stutter.
Forward stutter, or over stutter, one repeat unit length larger than the parent allele (N + 1 stutter), is a relatively rare product of the PCR amplification of STRs used in forensic DNA analysis. For all tetra and penta-nucleotide repeats, the current study found no correlation between allelic peak height, marker, or longest uninterrupted sequence in the allele. The data fit a gamma distribution with no explanatory variables. For the single trinucleotide repeat present in two of the four multiplexes (D22S1045) forward stutter is much more common and the best explanatory variable appears to be back stutter height. This suggests some fundamental co-causation of high backward and forward stutter for this locus. (Publisher abstract modified)

Date Published: November 1, 2014