Scientist refutes chromosome theory

October 07, 2004, vol. 31, no. 3
By Carol Thorbes

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A Simon Fraser University scientist's journey back into evolutionary time has led him and his colleagues to refute a longstanding hypothesis about the evolution of human chromosomes.

The threadlike linear strands of DNA include genes and other functional sequences, and are responsible for the transmission of hereditary information.

A team of researchers has discovered that chromosomal evolution, in particular evolutionary expansion of chromosomal functions, is more complex than first thought.

Cenk Sahinalp, a Canada Research Chair in computational genomics at SFU, and Can Alkan, one of his doctoral students, are on the team.

“Chromosomes are actually a hodgepodge of gene sequences from ancestral chromosomes that have evolved through duplication, amalgamation and deletion,” says Sahinalp.

“In the centromeric regions, which was the target of our study, we discovered rearrangement events in the last few million years, involving gene sequences from multiple chromosomes.”

(Centromeric is the central section of the chromosome.)

This contradicts an almost 30-year-old hypothesis.

It states that the composition of centromeric DNA is mostly the product of single chromosomes independently evolving through tandem duplications and point mutations over millions of years.

Prior to this study, scientists did not know that chromosomes exchanged centromeric DNA during evolution. “More advanced computer hardware and algorithms enable us to do complex computer simulations and calculations that are 100 times faster than possible even in the past year,” says Sahinalp.

“More main memory means we can unravel the layers of rearrangement events that have led to chromosomal evolution. It's like unwrapping an onion.”

And why bother unwrapping a 100 million year old onion that could make a scientist cry with frustration?

Scientists want to understand the evolutionary mechanisms underlying certain genomic diseases, an area of research that Sahinalp is pursuing.

This understanding lies in figuring out how gene sequences in lower species duplicated, migrated and evolved to the point where they formed the human genome.

Other members of the research team are the Evan Eichler lab at the University of Washington, and labs in the U.S. and Italy.

The international science journal Nature has published some of their findings at

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