Monday, 19 January 2015
Ancient, or prehistoric DNA (usually abbreviated to aDNA) has been of interest to palaeontologists ever since the remote possibility that it might be recovered began to be entertained. The improvement of molecular biological techniques such as the polymerase chain reaction (PCR) and the development of laboratory equipment for dealing with and sequencing DNA has greatly expanded the scope of possible research on aDNA, with the result that the field is presently one of active exploration.
Sadly, the breakdown of DNA from a dead organism, over long periods of time, leaves the original molecules separated into multiple short sections. These remnant sections may number only a few hundred base pairs out of hundreds of millions in the original sequence, and the remnant sections themselves may feature damage of various kinds. To recover a fragmentary DNA sequence from one chromosome in a fossil is thus a very long way from recovering an entire genome complete in every chromosome, just as the recovery of one sentence or even a word, is not the same as having the entire works of William Shakespeare. This matter of short sequences versus a complete genome is a primary separation of reality from Jurassic Park.
Another division between Jurassic Park’s scenario and reality is the durability of DNA, given it is truley the 'delicate molecule of life'. Can aDNA last for hundreds of millions of years? Ancient DNA studies were launched in 1984, when Berkeley researchers collected DNA from an 150 year old museum specimen of a recently extinct Zebra relative, the quagga (Equus quagga quagga). This was the beginning of a quest into the past for DNA, which had been thought to deteriorate too badly for study soon after death. Researcher Svante Paabo became a major pioneer of this field. He applied DNA extraction techniques to Egyptian mummies and other ancient human remains, successfully producing sequences from bodies thousands of years old. DNA from animals dead a few thousand years, such as extinct moas (Dinornis robustus and Dinornis novaezelandiae), has allowed for comparisons with living species in order to determine the evolutionary distance from living relatives.
When an organism shuffles off its coil, its DNA is subject to breakdown due to the nuclease enzymes naturally occurring within the cells, and the end result of this process if completed would be the complete reduction of DNA to mononucleotides, the links from which the chain was made. At that point all the DNA information would be destroyed. However, several factors can slow-down nuclease activity and DNA breakdown: cold temperatures, rapid drying, and salt are primary conserving influences. However, even under optimal conditions, DNA continues to break down through oxidation and other chemical processes, until finally its identity is erased or so blurred that it could have originated from a Blue Whale (Balaenotera musculus) or my brother (Stevenus manningii)!
So, once again we will creep toward a summer of speculation as folks claim to have dinosaur DNA in their impeccably preserved samples....but for me, if the movie sparks an interest in science for another generation, it has done a splendid job!