Scientists once hypothesized that chromosomal breakage and recombination occurred randomly along the chromosomes during evolution. But in 2003, a team from the University of California at San Diego and the Lewin laboratory reported that the breakpoints occurred more often in specific chromosomal regions than in others.
In 2004, Lewin and his colleagues reported a surprising finding: Breakpoint regions also contain a higher density of genes than other parts of the chromosome. In 2005, Lewin's team showed that breakpoint regions also have higher numbers of segmental duplications, a type of mutation that increases the copy number of genes and the sequences that flank them.
"To me, this was completely counterintuitive. I thought we would have these breakpoints in gene deserts," Lewin said. "We had to rethink the whole evolutionary hypothesis about what was going on in breakpoints."
In the new study, Denis Larkin, a senior scientist on Lewin's team, compared the chromosomes of nine mammals (human, chimp, macaque, rat, mouse, pig, cattle, dog, opossum) and a chicken. He found that the breakpoint regions contained many more copy number variants, insertions and deletions in their sequences than the other parts of the chromosomes. Such variations appear to make these regions more susceptible to breakage, Lewin said. (The chromosome analysis was facilitated by Evolution Highway, a powerful software tool developed in collaboration with Michael Welge and Loretta Auvil at the National Center for Supercomputing Applications at the University of Illinois.)
The researchers also found that different classes of genes appear in the breakpoint and break-re
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign