The yeast cells on the right harbor an extra copy of chromosome 4, which slows their division.

TORRES

A neupoloidy might not be a boon for cancer cells after all, say Eduardo Torres, Angelika Amon (Massachusetts Institute of Technology), and colleagues. Extra chromosome copies slow division, the researchers found.

Almost all tumors are aneuploid, and scientists have long suspected that the condition aids the renegade cells. Chromosome gain could provide extra copies of growth-promoting genes, and chromosome loss might jettison tumor suppressors. However, several studies, including work on cells from Down syndrome patients, suggest that aneuploidy inhibits cell proliferation.

To investigate aneuploidy's effects systematically, Torres and colleagues turned to mutant yeast that occasionally end up with spare chromosomes after mating. The researchers corralled cells that carried at least one extra copy of 13 of the yeast's 16 chromosomes. The fungi resembled cancer cells in their...

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