Forensic DNA evidence in question

How many times have we seen in TV series how they identify the murderer thanks to a DNA test a few hairs left behind by accident? Well, it seems that mitochondrial DNA testing, a forensic technique widely used today, is not as reliable as is assumed. An analysis revealed that cellular mitochondria can vary significantly between different tissues within the same individual, making comparison of samples misleading.

THE mitochondrial DNA comparison It has been part of police forensic analysis since the mid-1990s. Since there are so many mitochondria in every cell, readable copies of their genomes can be found even if the nuclear genome is damaged, since the two are in different compartments. For this reason, this process is very useful on old or heavily degraded samples. Hence so many stories in which a criminal is caught years later thanks to DNA analysis.

The reliability of this forensic technique is based on the assumption that the Mitochondrial DNA it does not vary much in the tissues of each individual. In other words, in theory, a subject's mitochondrial DNA is practically the same, regardless of the cell examined: a hair, a piece of skin, a bodily fluid. However, recent research has shown that every person can have a combination of several mitochondrial genotypes. His study revealed that a variant of DNA it was found in 7% of muscle mitochondria, but in 90% of kidney mitochondria. Until now, the fact that certain tissues had greater mitochondrial activity was attributed to the number of these, and not to the fact that they were different from each other.

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Based on the fact that not all cells have the same mitochondria, we should reconsider which parts of the DNA are conserved, and see if these can be used as a personal genetic fingerprint. Undoubtedly, this discovery would mean a serious setback for the world's best-known DNA comparison technique, as it would reduce its usefulness as a confirmatory test. A very serious puzzle awaits for forensic sciences.

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