We often shed small amounts of DNA when we talk, sneeze and touch things. ![]() They might investigate a break-in by swabbing the pry bar that was used to force a door, or they might swab a firearm that was used to commit a crime.īut such high sensitivity is a double-edged sword. Investigators might be able to solve a sexual assault, for instance, even if very little DNA were recovered. It is also a positive development because it allows forensic science to help solve a greater variety of crimes. This capability is an incredible technological achievement. Today, they can generate a profile from just a few skin cells that someone left behind when touching an object or surface. Forensic scientists once needed a relatively large amount of material, such as a visible blood or semen stain, to produce a DNA profile. Why have DNA mixtures and trace DNA become so prevalent?ĭNA methods have become extremely sensitive. So here’s a quick primer on DNA mixtures and trace DNA, what makes them difficult to interpret, and what these changes mean for the future of the field. Given the great weight that DNA evidence carries in the courtroom, it is important that lab analysts, criminal investigators, judges, attorneys-and anyone who might sit on a jury someday-understand these changes. More than just an upgrade to the existing tool set, these changes represent a fundamentally new approach to DNA evidence and mark a profound shift in the field. These more complex types of evidence make up an increasing share of the DNA casework in the United States, and labs are rapidly adopting new methods and tools to deal with them. ![]() With DNA mixtures and trace DNA, the results can be ambiguous and difficult to understand, sometimes even for the experts. With old-school DNA, the results tend to be clear cut: either a suspect’s DNA profile is found in the evidence or it isn’t, and nonexperts can readily understand what that means. These types of evidence can be far more difficult to interpret reliably than the relatively simple DNA evidence typical of earlier decades. They are also analyzing trace amounts of DNA, including the “touch DNA” left behind when someone touches an object. That profile, sometimes called a genetic fingerprint, can provide a solid lead in a case.īut DNA technology is always advancing, and in the last decade or so, forensic experts have been using new techniques to analyze DNA mixtures, which occur when the evidence contains DNA from several people. If the evidence contains sufficient DNA from just one or two people, forensic experts can often produce a clear DNA profile of the person or people who left it. DNA profiling is an extremely powerful tool for solving crimes.
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