from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A mammalian sex chromosome. Cells of females have a pair of X chromosomes while cells of males have an X and a Y.
Named by Hermann Henking in 1890 from x (signifying the unknown) due to some baffling properties he had observed. The brief resemblance in the appearance of the X chromosome to the letter "X" during cell division is entirely coincidental. (Wiktionary)