This majestic mammal roamed grassy plains of the Northern Hemisphere until it became extinct about 10,000 years ago. The scientific breakthrough allows for the first time comparion of this ancient species with today's populations of African and Indian elephants, not just at the level of mitochondrial sequences, but also encompassing information from the nuclear genome.
Analyzing organellar DNA from mitochondria has been the only method of studying ancient DNA in the past, as it is more tractable due to its 1000-fold higher copy number per cell. However, the mitochondrial genome codes for only a tiny fraction of an organism's genetic information -- 0.0006 percent in the case of a mammal. In contrast, most hereditary information is organized on chromosomes located in the cell's nucleus (nuclear DNA). A mammoth was chosen for study in part because of its close evolutionary relationship to the African elephant, whose nuclear DNA sequence has been made publicly available by the Broad Institute in Cambridge, Massachusetts (USA). Using comparisons with elephant DNA, the researchers identified 13 million base pairs as being nuclear DNA from the mammoth, which they showed to be 98.5 percent identical to nuclear DNA from an African elephant.
The project became possible through the discovery of exceptionally well preserved remains of a mammoth skeleton in the p ermafrost soil of northern Siberia, in combination with a novel high-throughput sequencing technique that could cope with the heavily fragmented DNA retrieved from the organism's mandible, its jaws. The bone material used in this study is approximately 28,000 years old, as was shown by beta-carbon dating analysis. This was a surprising finding, as it demonstrated that the analyzed material was frozen for more than 10,000 years before the maximum of the last ice age. The research team used a computational approach to demonstrate that an unprecedented 50 perecent of the bone DNA was indeed mammoth DNA, while the remaining genetic material was shown to belong to microorganisms living the tundra soil.
The study indicates that any organism that has been trapped in frozen ice or a permafrost environment for up to one million years will be an open book to the researchers. The search is now on for more specimens from plant, animal, and man that can illuminate the route evolution took on its way from the past to the present, and that can perhaps clarify the role environmental changes did play in the extinction of an entire species.
Initial funding for this study was provided by McMaster University, The Natural Sciences and Engineering Research Council of Canada, and Penn State University. The researchers now are seeking funding for the completion of the mammoth genome sequence and hope to conduct detailed comparative studies that include the genomes of African and Indian elephants.