3D models show chromosomes not X-shaped

The first 3D models of chromosome structure have overturned a long-held belief about their shape — the X chromosome looks nothing like an X! A new method for visualising chromosomes is painting a truer picture of their shape, which is rarely like the X-shaped blob of DNA most of us are familiar with, scientists say. The scientists at the Babraham Institute in UK, working with the University of Cambridge and the Weizmann Institute, have produced beautiful 3D models that more accurately show their complex shape and the way DNA within them folds up. The X-shape, often used to describe chromosomes, is only a snapshot of their complexity, the researchers said. “The image of a chromosome, an X-shaped blob of DNA, is familiar to many but this microscopic portrait of a chromosome actually shows a structure that occurs only transiently in cells — at a point when they are just about to divide,” Dr Peter Fraser of the Babraham Institute, said. “The vast majority of cells in an organism have finished dividing and their chromosomes don’t look anything like the X-shape. Chromosomes in these cells exist in a very different form and so far it has been impossible to create accurate pictures of their structure,” said Mr Fraser.