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Archive for September, 2015

Identical twins: can DNA tell them apart?

Tuesday, September 15th, 2015

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 (

Are Mouth Swabs Effective for Collecting DNA?

Tuesday, September 1st, 2015

Yes! Mouth swabs are not only effective for collecting DNA, they are the standard for many applications, including paternity testing, forensic testing, and many kinds of DNA identification. The cells collected from the mouth, preferably cheek cells, slough off in great quantity, and can be stored very easily.

If you’re in your 40’s, you might remember when blood was the only way to collect and find DNA. If there was a crime scene, the detectives needed blood—and hopefully a lot of it—to get a DNA profile. In paternity testing, blood was collected from each party, even infants, in order to compare DNA profiles.

Today, that’s all changed. Technology has changed, from a system called “RFLP” to one called “PCR,” and with that change, a much smaller amount of DNA is needed for DNA testing. In the PCR process, DNA is duplicated millions of times, so a little DNA can turn into a lot of DNA! With this change, a few hundred cells from the inside of cheek can be plenty to establish a DNA profile.

Here are some examples of programs that have been established to collect DNA profiles that you may not know about:

Military personnel. Those that join the military will have their DNA collected right when they join. It can be used to identify bodies when necessary.
Prisoner Inmates. Those that enter prison will have their DNA collected, often to compare their DNA to federal databases to link them to other crimes. The federal DNA database is called CODIS, or Combined DNA Index System.
Paternity Testing. States programs collect thousands of DNA samples every month for paternity testing for child support. DNA can now be collected very easily with cheek swabs, rather than blood samples. The use of cheek swabs for DNA collection has made it possible to even collect DNA at home, creating a new kind of paternity test, where people can find out who the father is without going through the state.

Mouth swabs that collect cheek cells are a very effective way to collect DNA. When dry, these swabs can be stored for decades, and the DNA can still be tested. With simple instructions, anyone can rub a swab on the inside of a cheek and collect enough DNA for a paternity test or any other DNA test. The swabs are not only effective, but they are THE chosen method by most state and federal agencies that collect DNA.

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