Epigenetics will help distinguish the DNA of identical twins
Since the beginning of its use in criminology in the 1980s, the DNA profiling method has become an indispensable tool for specialists involved in the investigation of various crimes. Recently, researchers from the University of Huddersfield, working under the guidance of Dr. Graham Williams, managed to overcome one of the limitations of this technology – they have developed an approach that allows you to distinguish the DNA or "genetic fingerprints" of identical twins.
The probability of a complete DNA match between two unrelated people is about 1 chance in a billion. For Siblings (siblings) it increases to 1 chance per 100,000. However, the nucleotide sequences in the DNA of identical (identical) twins are exact copies of each other. This greatly complicates the work of criminologists working to clarify the circumstances of the crimes in which the twins were involved. Due to the risk of punishment of an innocent person in such cases, it is often decided to abandon criminal prosecution.
According to Dr. Williams, methods for identifying the DNA of twins have been proposed before. One of them, known as "mutation analysis", involves the complete sequencing of the genomes of both twins to identify mutations that may have appeared in the genome of one of them. If such a mutation is detected, a targeted search is carried out in the biological material collected at the crime scene. However, this approach requires huge financial and time costs, which makes it unacceptable in the real working conditions of the forensic service.
The method developed by the authors is a much cheaper alternative that provides results in a short time. It is based on the concept of DNA methylation, which is actually a molecular mechanism that ensures the activation and inactivation of various genes.
During life, the severity of differences between identical twins increases due to the growth of differences between environmental factors affecting them. For example, one of the twins may start smoking or one will choose to work outdoors, while the other will work in the office. All this will cause various changes in the status of DNA methylation.
For a quick and relatively inexpensive analysis of differences in methylation statuses, researchers suggest using a method called "high resolution melting curve analysis" (from the English "high resolution melt curve analysis", (HRMA)".
The method consists in heating a DNA sample with a gradual increase in temperature until the melting point is reached, at which a complete rupture of hydrogen bonds occurs. The more hydrogen bonds DNA contains, the higher the melting point. If the DNA sequences differ in the degree of methylation, their melting temperatures will also differ accordingly. This difference can be quantified and used to identify the difference between identical twins.
At the same time, the developers admit that the new method has a number of limitations. The DNA of young twins raised under the same conditions may not have sufficient differences in methylation profiles. In addition, the implementation of the technique requires a sufficiently large amount of biological material, which is not always possible to obtain at the crime scene.
However, in any case, the proposed approach represents significant progress in the development of a relatively cheap and fast method for identifying differences between identical twins for forensic purposes.
Article by Leander Stewart et al. Differentiating between monozygotic twins through DNA methylation-specific high-resolution melt curve analysis is published in the journal Analytical Biochemistry.
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of the University of Huddersfiel:
Crime scene discovery – separating the DNA of identical twins.
24.04.2015