DIP–STR: A new marker for resolving unbalanced DNA mixtures

Abstract

The genetic characterization of unbalanced mixed stains remains an important area where improvement is imperative. Most cases of aggression, homicide and sexual assault produce biological traces with relatively large amount of the victim's DNA and small amount of the aggressor's DNA. If this ratio is smaller than 1:10 it is currently not possible to obtain a conventional autosomal DNA profile of the minor contributor, with potential loss of crucial DNA evidence. Y-STR analysis represents a solution for some cases but has several limitations. We propose here a method based on a new compound genetic marker formed by a Deletion/Insertion Polymorphism (DIP) linked to a Short Tandem Repeat polymorphism (STR), that we name DIP–STR. By means of allele-specific amplifications of DIP–STR haplotypes, we can produce a high resolution autosomal DNA profile of a donor that contributes less than 0.1% to a DNA mixture. Based on these features DIP–STR markers may outperform conventional Y-STR markers in mixed stain analysis.