Science for Kids
A recent success by geneticists shows that this may no longer be an impossible dream, but could at least become feasible.
Fossils, or more accurately, ancient DNA, have been seen as a way to access extinct animals, plants, and even humans. However, although small DNA fragments have been sequenced from potato remains, bears that lived in caves, and even Neanderthal fossils, the vast majority of samples were too damaged to be useful or were contaminated by foreign organic matter that had infiltrated them.
Two scientific papers published in Science and Nature at the end of last year fell like a bombshell in the world of paleontology. The articles announced that from 27,000-year-old mammoth remains found in Siberia, abundant and intact amounts of both nuclear DNA and mitochondrial DNA had been obtained.
The key to obtaining nuclear DNA from mammoth tissue samples is a brand-new DNA sequencing technique. Hendrik Poinar, a molecular evolutionary biologist from McMaster University in Canada, took bone samples from woolly mammoth fossils excavated from the perpetually frozen soil of Siberia and stored in an ice-filled cave. He observed that the samples he brought to his lab, particularly a jawbone, contained astonishing amounts of intact DNA. He sent these to Stanford University, which had developed a new device for genome sequencing.
The technique, developed to rapidly sequence large quantities of DNA, eliminates the need to implant DNA samples into bacteria to amplify and sequence them. Instead, researchers break the DNA into very small pieces, attach each one to a tiny bead, and place it inside a lipid (fat) bubble. Here, the DNA is copied numerous times for sequencing. Since each DNA fragment is isolated during the copying process, it prevents large amounts of “contaminant” DNA from bacteria or humans from leading to erroneous results.
The ancient DNA, which is extremely difficult to extract and sequence, was amplified and sequenced with extraordinary ease using the new method. Poinar says, “While we would have been happy with 10,000 mammoth base pairs, we obtained 28 million base pairs, 13 million of which belonged to the mammoth.”
A preliminary examination of the sequences revealed that the samples belonged to a female mammoth and that 98.55% of its DNA was identical to that of modern African elephants. Poinar’s team also found sequences from bacteria, fungi, viruses, soil microorganisms, and plants in the samples. Studying these will provide a better understanding of the mammoths’ natural environment.
In contrast, according to ancient DNA expert Svante Pääbo (Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany) and his team, who sequenced the mammoth’s mitochondrial DNA samples, the 17,000 base pairs found indicate that its closest relatives are Asian elephants.
