You may not be aware of it, but one of your chromosomes – the X chromosome – is considerably different from the rest and has posed a puzzle for scientists for over a decade. Early in mammalian evolutionary history, what is now the X chromosome was just like any of our other chromosomes. But at some point it evolved to be different. Unlike all other chromosomes, one of the two X chromosomes in women is inactivated in nearly all cells. It also has an extremely low mutation rate and – most perplexingly – the genes that are found on it are active in relatively few of our tissues. Now a study we recently published in PLOS Biology, has begun to shed light on what’s going on – by using a traffic analogy
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