Study: DNA accounts for only half the material in a chromosome

EDINBURGH, Scotland, Nov. 21 (UPI) -- Only half of each chromosome is made up of DNA material. An unexplained sheath accounts for most of the rest of the material inside a chromosome.

Until now, scientists assumed the vast majority of a chromosome was made up of DNA. Chromosomes are the slight structures inside each cell that hold an individual's genetic material.

The revelation was made possible by a new microscopy technique, called 3-D-CLEM, developed by scientists at the University of Edinburgh. Scientists were able to generate detailed 3D images of the chromosome and its insides using light and electron microscopy, as well as a sophisticated computer model.

Analysis of the images suggests between 53 and 70 percent of each of the 46 chromosomes is made up of DNA. The chromosome periphery material accounts for 30 to 43 percent.

"The imaging technique we have developed to study chromosomes is truly groundbreaking," Edinburgh researcher Daniel Booth said in a news release. "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."

Scientists aren't yet sure of the purpose of the remaining material, but hypothesized the sheath plays a role in protecting DNA and keeping it isolated during cell division. Previous studies have blamed errors during cell division for a variety of birth defects and cancers.

The latest findings, published in the journal Molecular Cell, will force scientist to reconsider their understanding of chromosome structure and the process of cell division.

"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," added Bill Earnshaw, a professor of biological sciences at Edinburgh.