Since any small trace of DNA can be amplified by PCR and then cloned or sequenced, some scientists have looked for DNA in fossils. Stretches of DNA long enough to yield valuable information have been extracted from museum specimens such as Egyptian mummies and fossils of various ages. In addition, DNA has been extracted from mammoth and plant remains frozen in the Siberian permafrost. This data has helped in studying molecular evolution and is discussed more fully in Ch. 20.
DNA may be amplified from fossil material and used in identification.
In the sci-fi best seller, "Jurassic Park", the DNA was not obtained directly from fossilized dinosaur bones. Instead, it was extracted from prehistoric insects trapped in amber (Fig. 23.21). The stomachs of bloodsucking insects would contain blood cells complete with DNA from their last victim, and if preserved in amber, this could be extracted and used for PCR. DNA has indeed been extracted from insect fossils preserved in amber. However, the older the fossil, the more decomposed the DNA will be. Normal rates of decay should break the DNA double helix into fragments less than 1,000 bp long in 5,000 years or so. So, though we will no doubt obtain gene fragments from an increasing array of extinct creatures, it is unlikely that any extinct animal will be resurrected intact.
PCR has been modified for rapid diagnosis by using fluorescent dyes to follow DNA accumulation.
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