Introduction: Dinosaurs and Jurassic Park (Genetics & Inherited Conditions)
Ancient DNA research is characterized as the retrieval of DNA sequences from museum specimens, archaeological finds, and fossil and mummified remains, as well as ancient microorganisms that were embedded in ice, rock, or amber, where only a miniscule amount of the original matter is present. For years, researchers struggled with their tiny and often degraded samples of ancient DNA, and the fruits of their labor were often equivocal.
In 1993, filmmaker Stephen Spielberg produced the highly popular motion picture Jurassic Park, based on Michael Crichton’s 1990 novel wherein scientists were able to bring dinosaurs to life using PCR and other biotechnologies. The film captured the imagination of the public as well as the scientific community, sparking renewed interest in ancient DNA. In a communication in 2009, Dr. Alan Cooper, at the University of Adelaide, Australia, noted that while is not possible to retrieve DNA from dinosaurs that became extinct more than 65 million years ago, per the unrealistic science of Jurassic Park (the upper limit of ancient DNA survival even under the most amenable, deep frozen conditions is approximately 500,000 years), genetic data gleaned from ancient DNA taken together with fossil records make it possible to study much older events by extrapolating backward.
As such, ancient DNA may be employed to study how species and populations evolved when...
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Isolation and Analysis of Ancient DNA (Genetics & Inherited Conditions)
The degree of DNA degradation of the ancient specimen is a function of age and the environmental conditions under which it was preserved; samples a few thousand years old will typically yield very viable DNA, while a woolly mammoth frozen shortly after death will yield more and better-preserved DNA than do the bones of a turtle that had weathered years before its demise. Of greater concern is that the ancient DNA may become contaminated with modern DNA; fossils and ancient remains (teeth and bones) are potentially at risk of contamination from pollen, bacteria, fungi, or the skin cells of the person extracting the DNA, and even minute quantities of modern DNA may contaminate the sample, resulting in faulty data. If the sample had been encased in ice or rock, contamination is unlikely; on the other hand, if the sample was exposed to air, contamination is highly possible.
Since ancient DNA is usually found in fossils in very small amounts, amplification with PCR is a necessity. However, contamination of ancient DNA is possible during the PCR process itself; erroneous nucleotides may be introduced and mistaken for mutations in the ancient DNA when compared to a sequence of modern DNA that is extant. Thus, the researcher must take special precautions to protect the specimen from contamination from the time it is extracted and isolated, through analysis including the PCR process, and during sequencing; upon...
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Ancient Microbial DNA (Genetics & Inherited Conditions)
One of the most fertile areas of ancient DNA analysis has been in the study of the origins of human diseases. In the past, archaeologists relied on physical evidence such as bone scars, deformities, and dental remains to determine whether an ancient human had suffered from a particular disease. More recently, the ability to recover ancient bacterial DNA from Egyptian mummies helped establish the presence of skeletal tuberculosis (TB) in finds dated as early as 3000 b.c.e. The bubonic plague, also known as the Black Death, which is caused by the bacillus Yersinia pestis, was thought to be responsible for a series of epidemics that occurred during the sixteenth century but could not be confirmed without adequate medical records. In 1998, however, French researchers unearthed the skeletal remains of persons who presumably died from the plague in the sixteenth century; using PCR to amplify a gene from Y. pestis extracted from dental pulp, along with sequencing, the scientists obtained proof that the plague did indeed exist at the end of the sixteenth century in France.
In 1999, Charles L. Greenblatt, at Hebrew University in Jerusalem, Israel, reported the isolation of DNA in several types of bacteria from 120-million-year-old amber. Comparisons of the DNA sequences of ribosomal RNA (rRNA) lent credence to the claim that he and his colleagues had actually isolated ancient DNA and not contaminants. While...
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Evolution and Ancient DNA (Genetics & Inherited Conditions)
Neanderthals, the closest relatives of modern humans dwelled in Europe and Asia until they became extinct approximately 30,000 years ago; for more than a hundred years, anthropologists and paleontologists have attempted to demonstrate their evolutionary relationship to modern humans, who emerged about 400,000 years ago. Dr. Pääbo made the first major contributions to the understanding the genetic relationship of modern humans to Neanderthals when he sequenced Neanderthal mtDNA in 1997. In 2009, Dr. Pääbo, who heads an international consortium of researchers called the Neanderthal Genome Project, announced that the group had completed a first draft of the complete Neanderthal genome, which can now be compared to earlier sequences of human and chimpanzee genomes in order to obtain initial insights as to how the Neanderthal genome differs from that of modern humans. The genome, generated from DNA extracted from the bones of three Croatian Neanderthal fossils, may help to elucidate the evolutionary relationship between humans and Neanderthals, as well as identify the genetic changes that enabled humans to migrate from Africa across the globe about 100,000 years ago.
Also in 2009, evolutionary anthropologists lent credence to the theory that a Neanderthal known as Shanidar 3 whose skeletal remains were unearthed in the late 1950’s and early 1960’s was killed by a human being who was capable of using a projectile...
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Future Research: New and Endangered Species, Climate Change (Genetics & Inherited Conditions)
In 2009, the International Union for Conservation of Nature estimated there are 8 to 14 million plants and animals in the world, of which only 1.8 million had been documented; every year, scientists across the globe discover new animal and plant species. Recently documented were an Ecuadorian salamander that resembles the film character E.T., a jumping spider, and the fossil of the oldest gecko species trapped in amber, dating back 100 million years ago. A flying frog, the world’s smallest deer, and an emerald green viper are among the more than 350 new species found in a decade of research in the eastern Himalayas; the discoveries from 1998 to 2008 put the region on par with the island of Borneo in Indonesia as a “biological hotspot.” The findings point to the importance of protecting the area, which covers northern Myanmar and India, Bhutan, Nepal, and Tibet. One can ask, however, how species are defined and why is it important to identify them.
In the nineteenth century, Charles Darwin studied species by observation using taxonomic systems: Did the animal have fur, fins, or feet? It was not until the early twentieth century that scientists began to compare the genetic differences among species. This led to the notion that a species could be defined by the barrier to reproducing with other species. However, since some species do not reproduce, one of the strongest notions...
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Further Reading (Genetics & Inherited Conditions)
Desalle, R., and D. Lindley. The Science of “Jurassic Park” and “The Lost World.” New York: HarperCollins, 1998. A critical look at the “science” used in the first two films based on Michael Crichton’s novels; for the nonscientist.
Jones, M. The Molecule Hunt: Archaeology and the Search for Ancient DNA. New York: Arcade, 2002. An overview of the history of ancient DNA analysis and other molecules.
Lane, N. Power, Sex, Suicide. Oxford, England: Oxford University Press, 2005. Follows the role of mitochondria throughout the life cycle.
Mithen, S. Singing Neanderthals. London: Weidenfeld & Nicholson, 2005. Presents theories on the origins of language and music.
Pennisi, E. “A Shaggy Dog History.” Science 298, no. 5598 (2003): 1540-1542. DNA extracted from ancient dog remains point to an Old World origin for New World dogs.
Teletchea, F. “Molecular Identification Methods of Fish Species: Reassessment and Applications.” Reviews in Fish Biology and Fisheries 19, no. 3 (2009): 265-293. Provides an overview of PCR methods for fish species classification.
Wayne, R. K., J. A. Jennifer, and A. Cooper. “Full of Sound and Fury: The Recent History of Ancient DNA.” Annual Review of Ecology and Systematics 30 (1999): 457-477. Includes excellent examples in which DNA originally thought to be “ancient” was found to...
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