Chromosomes, long believed to be passive cargo when cells divide, actually control some aspects of the critical life process itself, according to a report recently published in the journal Nature by UC Davis researchers. Scientists have regarded chromosomes in dividing cells as corpses at a funeral -- the reason for the proceedings, but not active participants. Researchers say the study demonstrates for the first time that chromosomes play an active role, more akin to the quarterback than the football, in controlling cell division. During the process critical to growth and reproduction, a cell must pass a series of checkpoints where it pauses to determine its readiness to begin or continue cell division. Until recently, all of these checkpoints were believed to depend on cellular proteins and enzymes. Post-doctoral fellow Kim S. McKim and his associates found that during the process where cells divide to make egg cells (also known as "gametes") the chromosomes controlled the cell's ability to pause at a crucial checkpoint. "Because this checkpoint may play an important role in ensuring the production of normal gametes, this finding may be significant for the study of birth defects such as Down's syndrome," says R. Scott Hawley, a professor of genetics at UC Davis and senior author of the paper.