BIRTH defects such as Down's syndrome may be due to a defect in a protein that ensures that sperm and egg cells get the right number of chromosomes, say Marion Shonn and her colleagues at the University of California in San Francisco.
When cells divide, the duplicate sets of chromosomes are pulled apart by spindle fibres. Checkpoint proteins make sure that the chromosomes are properly attached to the spindle. Shonn's team has found that a yeast checkpoint protein, mad2, plays a critical role in the type of division that produces sperm and eggs. If it is faulty, cells produce spores with either too many or too few chromosomes (
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