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

(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.

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.)

This NIH's National Cancer Institute image shows the 46 human chromosomes in blue.
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)
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