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Identical twins: can DNA tell them apart?

Advancements in DNA technology has made DNA analysis a revolutionary tool in forensic investigations. Since its breakthrough in the 1980s, DNA is used for identification of individuals in crime scene evidence, unknown human remains, and biological relationships. However, one limitation has been the ability to distinguish between identical twins. Since identical twins present exactly the same DNA profile as each other, their DNA is indistinguishable from each other. Legal conundrums result because it is not possible to tell which of the twins was guilty or innocent of the crime. Rather than risk convicting the wrong person, prosecutors drop charges and a potential criminal is set free.

A new solution to this problem has developed by the Forensic Genetics Research Group at the University of Huddersfield. Led by Dr. Graham Williams, their findings have been published in the Analytical Biochemistry journal. The method is based on the concept of “DNA methylation,” which is effectively the molecular mechanism that turns various genes on and off. The research shows that as twins age, the degree of difference between them grows as each is subjected to different environmental conditions. For example, one twin may be a smoker, one may work outdoors, one may work at a desk. The methylation status of their DNA will thus evolve, making close inspection of the DNA able to reveal the difference between the two individuals. Heretofore the only method proposed for distinguishing the DNA of twins was “mutation analysis”, but this was considered too costly for use in police investigations. Dr. Graham and his team have developed a more cost-efffective method based on this concept, and he explains it this way: ” ‘High resolution melt curve analysis’ or “HRMA” subjects the DNA to increasingly high temperatures until the hydrogen bonds break. This melting temperature may vary between the twins, and therefore the more hydrogen bonds that are present in the DNA, the higher the temperature required to melt them. Consequently, if one DNA sequence is more methylated than the other, then the melting temperature of the two samples will differ-a difference that can be measured, and which will establish the difference between the two identical twins.” Dr. Graham further explains that there are limitations to this solution. First, the technique requires a high quantity sample that may not be present in crime scene evidence. Also, the younger the twins and those raised in highly similar environments, the less likely the development of the methylation differences.

This research demonstrates that scientific breakthroughs continue to offer society more and more tools to solve crime. A detailed summary of the science behind the breakthrough can be found at the blog-site The Conversation (http://theconversation.com/new-dna-technique-means-pointing-the-finger-at-the-right-identical-twin-just-got-easier-39332).

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