Universal Strategy to Interpret DNA Profiles That Does Not Require a Definition of Low-Copy-Number

• NCJ Number: 231564
• Journal: Forensic Science International: Genetics Volume: 4 Issue: 4 Dated: July 2010 Pages: 221-227
• Author(s): Peter Gill; John Buckleton
• Date Published: July 2010
• Length: 7 pages
• Publication Format: Article
• Publication Type: Report (Study/Research)
• Language: English
• Country: Ireland

Annotation

This paper critically examines the causes of the underlying confusion relating to low-template (LT) DNA profile interpretation.

Abstract

The authors note there has been much confusion associated with the meaning of low-copy-number (LCN). The phrase is typically used to describe a technique that uses elevated cycle number or, to a lesser extent, increased injection time; however, the authors reject this definition, because the stochastic effects associated with the analysis of LT-DNA, including analysis by LCN, are observed with all DNA profiling technologies. They argue that the rationale applied to LT-DNA profiles should be applied equally to all DNA profiles, regardless of the method used to produce them. The authors note that is difficult to distinguish between LT-DNA and conventional DNA because there is no discrete "cut-off" point that can be reasonably defined or evaluated. LT-DNA is loosely characterized by "drop-out" (alleles may be missing) and "drop-in" (additional alleles may be present). The authors indicate they have previously described probabilistic methods that can be used to incorporate these phenomena using likelihood ratio (LR) principle. They prefer this to the random-man-not-excluded (RMNE) method, because a coherent way forward cannot be provided within the restrictions set by this framework. Most LT-DNA profiles are interpreted using a "consensus" profile method, which the authors call the "biological model." Under this model, only those alleles that are duplicated in consecutive tests are reported. The authors recognize that there is an increased need for probabilistic models to take precedence over the biological model. These models are required for all kinds of DNA profiles, not just those believed to be low-template. The authors suggest education and training in the methods they recommend, so they can be widely introduced. 1 figure and 49 references