Ancient DNA (aDNA)

Ancient DNA is DNA that has not been specifically or intentionally preserved by humans.  aDNA basically refers to DNA that has been found in fossils and bones.  The quality of aDNA is often denatured, sometimes it is severely degraded while other times it could be considered in better condition.  The condition it is found in is heavily dependent on the history of the specific DNA strand and the environment in which it was present.  Our knowledge of aDNA is increasing very rapidly, wheareas a little over decade ago aDNA was nearly useless to scientific studies.  We have also learned what preserves DNA and what cannot, unfortunately to Jurassic Park fans amber is not a very good way of preserving DNA.  It seems that in the early 1990’s, even scientists thought amber was a very good preserver for DNA.  This could have to do with how well preserved species physically appear in amber fossils and early tests had scientist’s believing they recovered fully intact DNA strands.  However, during this time, contamination was more unknown and those extracting the aDNA did not take proper precautions to obtain the aDNA, also due to the science being younger and technology not being as advanced, they were unable to differentiate between contaminated strands and actual aDNA.

So where can we obtain aDNA?

We have learned that heat much more rapidly denatures or degrades DNA and that freezing tissue can preserve DNA very well.  This is how the Frozen Zoo in San Diego is planing on studying extinct species.  This is also why we are able to find better samples of aDNA in the arctic regions.  While, specimens found in hot and humid climates tend to be to degraded to obtain useful aDNA.

How is aDNA useful? Especially if it is denatured?

As I mentioned, aDNA has recently become much more useful, but how is it useful if aDNA inherently is not fully intact.  Well, over the past decade or so we have very much advanced both our understanding and technology involved with DNA and genomes.  We can much more efficiently and much more quickly sequence genomes of species or even aDNA fragments.  The sequenced aDNA is then able to be compared to the DNA of close extant relatives of that species.  For example, the band-tailed pigeon is extant, or still alive, so we can easily map out the genome of the band-tailed pigeon.  Then we can take tissue samples from the extinct Passenger Pigeon, whose DNA has never been preserved properly, and this aDNA from the Passenger Pigeon can be compared to the DNA of the band-tailed pigeon.  We can then fill in these gaps in DNA by using the close relative band-tailed pigeon.  This particular example can be further read here.

^ Modern aDNA attire, which minimizes chances of contamination.