Day 164 (Xpter-Xp22.31): Chromosome X, named for mystery not shape


Day 164 has 32 protein-coding genes (browser view) and is the beginning of Chromosome X. Like the other tip of X, this is a pseudoautosomal region.

Per Wikipedia:

It was first noted that the X chromosome was special in 1890 by Hermann Henking in Leipzig. Henking was studying the testicles of Pyrrhocoris and noticed that one chromosome did not take part in meiosis. Chromosomes are so named because of their ability to take up staining. Although the X chromosome could be stained just as well as the others, Henking was unsure whether it was a different class of object and consequently named it X element,[14] which later became X chromosome after it was established that it was indeed a chromosome.[15]

The idea that the X chromosome was named after its similarity to the letter “X” is mistaken. All chromosomes normally appear as an amorphous blob under the microscope and only take on a well defined shape during mitosis. This shape is vaguely X-shaped for all chromosomes. It is entirely coincidental that the Y chromosome, during mitosis, has two very short branches which can look merged under the microscope and appear as the descender of a Y-shape.

Click here to see all 8668938 letters of Day 164.

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