Every human cell carries 46 chromosomes, the DNA-and-protein packages that transmit genes from generation to generation as cells divide. Lately, scientists have been wondering whether they can fool the machinery of the cell by inserting a synthetic 47th chromosome furnished with genes of their own choosing. Two companies, Athersys in Cleveland, OH, and Chromos Molecular Systems in Burnaby, British Columbia, are beginning to find an answer; they are testing artificial chromosomes as a safe and effective way to introduce therapeutic genes into patients suffering from deadly genetic disorders.

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