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!
