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Ancient DNA could tell a lot of different stories
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Information or “recipe” for every living organism is contained in DNA material (or RNA, in some viral species). DNA is composed of nucleotides aligned in two chains that bond together through complementary base pairing. Result is typical double helix shaped molecule. Every living creature should be proud of his uniqueness - there aren’t two individuals (except identical twins) that have the same DNA. Thanks to that fact, molecular fingerprinting is used for identification of the single individual, forensics can identify suspects, and paternity test could be performed … Growing number of experiments use DNA for gathering different kind of information. Since DNA material is able to survive long period of times, excavation of the various plant or animal remains could tell us a lot of different stories about past on the Earth.

Ancient DNA represents DNA material extracted from old biological samples. Unlike classical DNA analysis, these specimens are of less quality. Archeological discoveries of different animal and plant materials precede DNA analysis. Even though DNA is present in each cell of the living organism, decomposition of the body after death limits the sources that could provide sufficient DNA for the further analysis. In the rare situations when body is entrapped in the ice or amber, high quality and quantity DNA is available. Various insects, plants and bacterial species were successfully investigated after DNA was extracted from amber entrapped specimens. For animal species, usual source of DNA are bones and teeth. Weather conditions (especially temperature and moisture) greatly affect the speed of DNA decay. At temperature of -5 Celsius, mitochondrial DNA is degraded to 1 base pair after 6.830.000 years. Degradation of the nuclear DNA is two times faster than mitochondrial. Using PCR method, scientists were able to multiply and investigate some very old samples dating back from Cretaceous period (145-66 million years ago). Not all ancient DNA samples are million years old. Some ancient DNA analysis investigates remains of much younger origin.

One recently published article investigates climate changes based on analysis of the ancient urine. Rock hyrax is cute little creature that looks like a rodent but is actually more closely related to the elephant. They inhabit rocky environment in Sub-Saharan Africa and Middle East. These social animals have specially designated area serving as mutual (communal) toilets. They are used for years, containing urine samples of a lot of hyrax generations. Urine crystallizes in time, forming stratified accumulations known as middens. Scientists found well preserved 10 thousands year old African middens that could provide more insight in climate changes associated with the hyrax habitat. Collected samples were investigated for organic molecules, metabolites and plant derived molecules. Forensic DNA analysis provided more information on the type of diet they have in the past revealing what plants were available 30.000 years ago. Since plant species are typical representatives of the each climate zone, list of available species on the hyrax menu precisely inform scientist which climate type existed 30.000 years ago. Middens were used for pollen analysis as well. That analysis increased the accuracy of predicted climate type. Given results showed that southern African climate underwent series of complex climate changes after last ice age (~20 000 years ago). Future experiments will investigate changes middens undergo when exposed to computerized simulations of past climate changes. Scientists are hoping that provided information would be helpful in revealing mysteries behind fast and unpredicted weather changes in this dynamic environment.

Another location and another set of animal excrements also provided evidence on previously lived flora and fauna. North West area of Australian continent is arid and any kind of old DNA is hard to find. However, scientists managed to found 700 - 30.000 years old samples of urine, fecal matter, hair, bones and eggshells cemented together in three locations. Different species (now extinct common brushtail possum and various arid grasses) that inhabited Western Australia were easily detected thanks to genetic analysis. Previous investigations focused on carbon dating, macrofossils and pollen identification; DNA analysis expanded previous data and helped in creating final image of the environment from the past.

Analyses of this kind are especially important for endangered species. Future conservation plans and efforts will work better if scientists become fully familiar with extinct species and be able to compare existing environmental data with the ones from the past.
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Ancient DNA could tell a lot of different stories - by BojanaL - 12-01-2012, 09:12 PM



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