DIP-STR markers: a new tool for the alalysis of unbalanced mixtures of DNA from two individuals

Developers

v. Castella, J. Gervaix, D. Hall.

Description of the technology

In forensic science, the genetic characterization of unbalanced mixed stains remains an important area where improvement is imperative. Most cases of aggression, homicide and sexual assaults are likely to produce bio¬logical traces with a relatively large amount of the victim’s DNA and a 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 consequential loss of potentially crucial DNA evidence.

To address this recurrent problem, Swiss scientists developed an original method based on a new compound genetic marker formed by a Deletion/ Insertion Polymorphism linked to a Short Tandem Repeat polymorphism, that we named DIP-STR. With this compound locus, the scientists designed allele specific primers. DIP-STRs were found highly polymorphic and widespread in the genome. They require standard genotyping techniques as for currently used STR markers. The scientists described a preliminary list of DIP-STR loci and their performance at casework resolution of both simulated and real samples.

Practical application

This novel analytical approach allows for the unambiguous genotyping of a minor component in the presence of a major component, where DIP-STR genotypes of the minor were successfully procured at ratios up to 1:1,000.

Laboratories

• Forensic Genetics Unit, University Center of Legal Medicine Lausanne and Geneva, (Switzerland)

Links

Publications

• Castella, Vincent, Joëlle Gervaix, and Diana Hall. «DIP-STR: highly sensitive markers for the analysis of unbalanced genomic mixtures." Human mutation 34.4 (2013): 644–654.
• Hall, D., and v. Castella. «DIP-STR: A new marker for resolving unbalanced DNA mixtures." Forensic Science International: Genetics Supplement Series 3.1 (2011): e1-e2.
• Cereda, G., et al. «An investigation of the potential of DIP-STR markers for DNA mixture analyses." Forensic Science International: Genetics 11 (2014): 229–240.
• Cereda, G., et al. «Object-oriented Bayesian networks for evaluating DIP-STR profiling results from unbalanced DNA mixtures." Forensic Science International: Genetics 8.1 (2014): 159–169.
• Oldoni, Fabio, Vincent Castella, and Diana Hall. «A novel set of DIP-STR markers for improved analysis of challenging DNA mixtures." Forensic Science International: Genetics 19 (2015): 156–164.