Freeze-dried chromosomes can survive for thousands of years
For palaeontologists, DNA is infuriatingly fragile. Its long chains begin to break apart shortly after death, destroying valuable information about the deceased parent organism. Unlike bones, footprints and even faecal matter, which can comfortably survive—in fossilised form—for millions of years, DNA rarely lasts much more than a hundred. In recent decades scientists have discovered that some exceptionally well-preserved bodies do still have readable fragments of genetic code hundreds of thousands of years after death. But these have been tiny scraps. They lack much of the valuable information that an intact genome provides.
A major advance may be at hand. A new paper in Cell, a scientific journal, describes the discovery of fossil chromosomes—coiled-up strands of DNA millions of base pairs long—inside the cells of mammoths that died tens of thousands of years ago. The research “really opens a door for a new kind of exploration of ancient life”, says Erez Aiden of the Baylor College of Medicine (BCM) in Houston, Texas, who is one of the paper’s lead authors.
DNA is a resolutely three-dimensional molecule. In animals and plants, long strands are coiled and folded into chromosomes, which store genetic information inside the nucleus of a body’s cells. The architecture of those chromosomes is as important as their content. It enables interactions between specific strands of DNA and regulatory proteins in the nucleus, thus determining which genes are expressed in different cells and tissues. Snippets of DNA recovered from ancient specimens lack this valuable information. Given the structural complexity of a chromosome, the chances of ever finding one were deemed to be extremely slim.
