Sequencing reveals origins of X chromosome
The complete sequence of the human X chromosome was published in Nature this week. The work, led by Mark Ross at the Sanger Institute in Cambridgeshire, UK, shows that large segments of it match parts of normal chromosomes in birds, confirming the X chromosome's "non-sex" origins. Despite the fact that X is much larger than the tiny Y, it seems that both evolved from a pair of conventional chromosomes in early mammals sometime in the past 300 million years - an idea first proposed in 1967.