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Q and A: Can the ME Match Hair Samples Taken 10 Years Apart?

23 Dec

Q:    Will hair samples taken ten or more years ago (like from a haircut) match current samples taken from the subject? For instance, could a tech using a comparison microscope be able to tell if they came from the same individual or would time have altered the person’s hair too much to tell except through DNA testing? (The subject is male, if it makes a difference.) And would there still viable DNA from the old sample to
make a DNA comparison to the new sample?

TMS, Florida

A:    Hair matching depends upon the physical characteristics of the hair shaft. The shaft of the hair possesses three parts. The central core is called the medulla, the surrounding portion the cortex, and the thin outer coating the cuticle. It’s similar to the number 2 yellow pencil you used in school. The lead would be the medulla, the wood the cortex, and the yellow paint the cuticle. The examiner looks at each of these areas when he attempts to match two hairs.


These characteristics are mostly stable, but color can change with aging, as hair turns gray in some people. But the make-up of the medulla and the pattern of the cuticle are stable. In a young or middle-aged person, the hair would not change a great deal over 10 years. Of course, treatments and coloring agents can make the examiner’s job more difficult but he still should be able to make a match.
Hair is predominantly class evidence. The examiner can say that two hairs are consistent with having come form the same person, but that’s about as far as he can go. But there are circumstances where hair can supply DNA, which is highly individualizing


Hair production and growth occur when follicular cells die, loose their nuclei (and DNA), and are incorporated into the hair shaft. This means that the hair shaft is composed of cellular debris and possesses no nuclear DNA. The follicle (bulb) is composed of living cells, which do possess DNA. If the hair has follicular tissue attached this can serve as a source of DNA, which can be used for fingerprinting and matching.
But what if the hair has been cut, as in your scenario, or has fallen out and has no attached follicle? Often, mitochondrial DNA (mtDNA) can be extracted from the hair shaft. Since the hair is built from cellular remnants, and since the cell cytoplasm houses mtDNA, it is possible to obtain a usable sample of mtDNA from the shaft of the hair. Mitochondrial DNA is passed down the maternal line unchanged and can be used to identify the maternal ancestry of the person in question. Often this is enough to make a positive ID.
For example, if the mtDNA of a hair found at a crime scene matches that from hair taken from the suspect’s siblings or other maternal-line relative (mother, grandmother, etc.) it proves that the person shedding the hair at the scene shared a maternal linage with the suspect’s relatives. This means that either he was there or one of his relatives was. Since Granny didn’t likely commit the crime, he must have. This evidence is not as strong as a nuclear DNA match but it is very powerful.


In your scenario, if nuclear DNA can be obtained from the bulbs of the two hairs, then an absolute match can be made. If mtDNA is all that is available and if the mtDNA matches, the examiner can say that the two hairs were shed by individuals who shared the same maternal linage. Or, as in your case, the hairs came from the same person. If the mtDNA and the physical characteristics both matched, this would be powerful evidence that the hairs came from the same person. Not absolute, but strong.

 
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Posted by on December 23, 2010 in DNA, General Forensics, Q&A

 

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