Evolutionary forensics: DNA survives in Mammoth’s hair
Hair is one of the first things police investigators look for when searching for evidence at a crime scene because DNA can be recovered from it, and DNA can lead the officers to convict or clear a suspect. In most cases, hair strands are recovered within a few days and DNA is still in good shape. But what about the DNA that has been sitting for longer? Say about 25,000 years?
Scientists refer to DNA that comes from fossils or archaeological samples as “ancient DNA”. The range of time within which DNA can be recovered and still be useful for analysis is very wide, but depends a lot on the nature of the sample and the conditions under which the DNA spent the time. In many cases, DNA that is several thousands years old has been successfully analyzed. Mammoths no longer exist, but they have been around until about 10,000 years. Even though is not a long period of time in evolutionary terms, it can be long enough to allow complete degradation of DNA molecules in normal conditions of exposure. However, these beasts used to live in places that underwent very low temperatures since the time they disappear making it likely for substances like DNA to survive relatively intact.
Analysis of hair from some mammoths suggests that hair samples may contain enough genetic material to allow studying portions of the animal’s DNA. Even though each animal cell contains huge amounts of DNA in their nucleus, scientists are more interested in recovering the DNA from the mitochondrial genome. A few reasons are that mitochondrial DNA is far more stable (resistant to degradation), there are many copies of it in each cell, and is more useful to the kind of research that sheds light in the evolution of these animals and their phylogenetic relationships to existing animal groups.
Bones are another source where scientists look for ancient DNA. However, bones are more prone to bacterial contamination than hair tissue. Any remaining DNA is locked inside the hair follicle and bacterial and fungal contaminants can be washed away with a solution containing bleach. Researchers from the University of Copenhagen have just reported the sequencing of the complete genome of the mitochondrion obtained from hair samples of a 41,000-year-old mammoth found in 1806 in Russia, being one of the oldest specimens studied so far with this methodology.
A remarkable point is that DNA was successfully recovered even though the mammoth body was stored at room temperature for more than a century. This will prompt biologists to turn to museums to find valuable DNA specimens that will greatly improve our understanding regarding myriads of questions on biology, ecology evolution and so on.
