An advanced imaging technique combining light and electron microscopy with computational modeling software has revealed that DNA makes up only half of the material inside chromosomes — far less than was previously thought. Researchers at the University of Edinburgh developed the precise microscopy technique — known as 3D-CLEM — to produce detailed 3D models of all 46 human chromosomes. Analysis of the images reveals that material containing DNA and supporting proteins, called chromatin, accounts for between 53 and 70 percent of the total contents of chromosomes. The remaining 30 to 47 percent is composed of the chromosome periphery, a mysterious sheath that surrounds the genetic material, researchers say. The study was co-led by Daniel Booth and Bill Earnshaw of the University of Edinburgh's School of Biological Sciences. Booth said, "The imaging technique we have developed to study chromosomes is truly groundbreaking. Defining the structure of all 46 human chromosomes for the first time has forced us to reconsider the idea that they are composed almost exclusively of chromatin, an assumption that has gone largely unchallenged for almost 100 years." "We now have to re-think how chromosomes are built and how they segregate when cells divide, since the genetic material is covered by this thick layer of other material, " said Earnshaw . The study was published in the journal Molecular Cell.