Forensic DNA analysis, a cornerstone of modern criminal investigations, may be less reliable when dealing with DNA mixtures from populations with low genetic diversity, according to researchers from the University of Oregon. Published in iScience, the study highlights the potential for false positives in these cases, raising concerns about the implications for justice systems.

The Challenge of DNA Mixture Analysis

Modern DNA analysis techniques are highly sensitive, capable of detecting trace amounts of DNA left behind by skin cells or other minor biological material. While this sensitivity enables forensic scientists to analyse complex DNA mixtures, such as those found on frequently touched objects like door handles, it also increases the risk of errors.

“DNA mixture analysis can be extremely powerful, but its accuracy depends on the genetic diversity of the population involved,” said Rori Rohlfs, lead researcher and data scientist at the University of Oregon. “Groups with fewer genetic variants are more likely to produce false inclusions, especially when analysing mixtures with multiple contributors.”

The team used existing genetic databases to study the frequency of genetic markers across various populations. By simulating DNA mixtures from different genetic backgrounds, they found that populations with lower genetic diversity—such as certain Indigenous, Latine, or Pacific Islander groups—were more prone to false positives. The likelihood of error increased further with the number of DNA contributors in a mixture.

Ethical Challenges in Genetic Research

Rohlfs’ team faced additional challenges regarding the ethical sourcing of genetic data. Many historical genetic studies did not obtain informed consent, particularly when collecting samples from vulnerable groups such as incarcerated individuals. To maintain ethical standards, the team only included data from sources where informed consent could be verified, limiting the scope of their analysis but ensuring integrity.

The study also cautions against oversimplified assumptions about genetic ancestry. Labels such as race and ethnicity often fail to accurately reflect the genetic diversity within populations, complicating the interpretation of forensic results.

Implications for Forensic Science

While the study does not claim that DNA analysis is universally unreliable for certain groups, it emphasises the need for caution when interpreting DNA evidence in cases involving populations with low genetic diversity. The findings highlight the importance of understanding the limitations of forensic tools to avoid wrongful convictions.

Rohlfs is now expanding her research at the University of Oregon, focusing on the accuracy of emerging forensic DNA techniques. “We’re still in the early stages of understanding how ancestry influences forensic analysis,” she said. “Our goal is to develop methods that minimise errors and ensure fairness across all populations.”

This research sheds light on the complexities of DNA analysis and underscores the need for continued scrutiny and refinement of forensic tools to uphold justice in diverse societies.

Republished courtesy of the University of Oregon.

Note content has been edited

https://news.uoregon.edu/limits-forensic-dna-analysis