X Chromosome Actually Looks Nothing Like an X

It's more like a lumpy blob of spaghetti
By Arden Dier,  Newser Staff
Posted Sep 28, 2013 6:57 AM CDT
X Chromosome Actually Looks Nothing Like an X
This NIH's National Cancer Institute image shows the 46 human chromosomes in blue.   (AP Photo/NIH, National Cancer Institute, Hesed Padilla-Nash, Thomas Ried)

(Newser) – Here's your fun fact for the day: Contrary to popular belief, the X chromosome isn't shaped like an X at all—something that scientists have actually long been aware of. What they haven't known, however, is what that shape is ... until now. Per a paper published in Nature, the first 3D model of the chromosome has been made using measurements taken of the X chromosome in mice, and it depicts what LiveScience likens to "amoebas" and "lumpy blobs"; the Christian Science Monitor prefers "a heap of threaded-up vermicelli." The model, which is tinier than a red blood cell, provides a "map of how the chromosome folds, which parts touch and where, and who is next to who," explains paper author Peter Fraser.

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Before sharing the implications of this, the Monitor gives some interesting history: The "X" designation started as a placeholder in 1890 ("X" as "unknown") and turned out to be a temporarily appropriate moniker: In the instant before cells divide (high-school biology refresher: we're talking about mitosis), the splitting cell's soon-to-be-two-cells pull away from each other while attached at the middle, giving an X appearance. But only .01% of your cells are dividing at any given time; the rest of the time things are more blob-like, and the new model will help scientists better understand which of the X chromosome's 153 million base pairs actually sit next to each other in their pasta-like state. Why this is a big deal: Scientists should be able to better study which of the many bundled-together regions of the chromosome are related to things like aging and disease. (Another discovery reported this week is more galactic—a surprising amount of water on Mars.)

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