An international team including researchers from the National Human Genome Research Institute (NHGRI) has discovered that mammalian chromosomes have evolved over tens of millions of years by breaking at specific sites rather than randomly, as had been widely thought.

Writing in last week’s Science, the researchers compared the genomic architecture of eight mammals: human, mouse, rat, cow, pig, dog, cat and horse. Bioinformatics analysis revealed that during evolution, the chromosomes are rearranged by breaking typically in specific locations, rather than in a random fashion, as had been widely thought. “This study shows the tremendous power of using multi-species genome comparisons to understand evolutionary processes, including those with potential relevance to human disease,” comments Eric Green, NHGRI Scientific Director.

Inherited chromosomal translocations play a key role in evolution by rearranging genetic material, which in rare cases can be beneficial. They can also be deleterious – translocations are often associated with cancer. The researchers find that the chromosome breaks linked to cancer are more likely to occur in proximity to the evolutionary breakage hotspots. The authors also conclude, based on computer-generated reconstructions of the genomes of long-extinct mammals, that there was a sharp increase in the rate of chromosomal evolution among mammals following the demise of the dinosaurs some 65 million years ago.

Authors include Harris Lewin (University of Illinois at Urbana-Champaign) and William J. Murphy, Ph.D., of Texas A&M University in College Station. Other study participants were from the National Cancer Institute, the Genome Institute of Singapore and the University of California at San Diego.

Murphy, W.J. et al. “Dynamics of mammalian chromosome evolution inferred from multispecies comparative maps.” Science 309, 613-617 (2005).