Female mammals have two X chromosomes, but males only have one. Early in development, the female embryo must shut down one X chromosome in every cell, or an overdose of the genes on those chromosomes will kill her.
Scientists haven’t worked out all the details of X inactivation, and a new study prolongs the puzzlement. A gene that scientists have found to regulate X chromosome activity in mice doesn’t work in people, report researchers from the Johns Hopkins Medical Institutions in Baltimore.
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