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• X chromosome
  X chromosome

  noun

  a sex chromosome of humans and most mammals that determines femaleness when paired with another X chromosome and that occurs singly in males.
• X-chromosome
  X-chromosome

  noun

  the sex chromosome that occurs in pairs in the diploid cells of the females of many animals, including humans, and as one of a pair with the Y-chromosome in those of males Compare Y-chromosome

X chromosome

American  

noun

Genetics.

1. a sex chromosome of humans and most mammals that determines femaleness when paired with another X chromosome and that occurs singly in males.

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X-chromosome British  

noun

1. the sex chromosome that occurs in pairs in the diploid cells of the females of many animals, including humans, and as one of a pair with the Y-chromosome in those of males Compare Y-chromosome

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X-chromosome Scientific  

/ ĕks′krō′mə-sōm′ /

1. The sex chromosome that in female mammals is paired with another X-chromosome and in males is paired with a Y-chromosome. Very few genes on the X-chromosome have counterparts on the Y-chromosome, and since males have only one X-chromosome, any gene present on it (even if the gene is recessive in females) is expressed in males. In females, one of the two X-chromosomes in each cell is deactivated.

2. See more at sex chromosome See note at sex

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Etymology

Origin of X chromosome

First recorded in 1910–15

Example Sentences

See Examples For:

X chromosome X-chromosome

The team analyzed modern human DNA preserved in Neanderthals, and found an abundance on the X chromosome -- the mirror opposite of humans.

From Barron's ● Feb. 26, 2026

"In this study, we successfully assembled the first complete cattle X chromosome and four autosomes. However, assembling the remaining chromosomes to the same level of completeness remains an aim for future work," Dr. Low said.

From Science Daily ● Jan. 12, 2026

Researchers suspected that the mutation causing the condition was somewhere on the X chromosome, because females, which have two X chromosomes, are less affected.

From The Wall Street Journal ● Oct. 6, 2025

The abnormal IP gene is located on the X chromosome.

From BBC ● Apr. 19, 2025

Any egg fertilized by a Y-bearing sperm will become a male with white eyes because the only X chromosome that the male contains comes from his mother and is white producing.

From A Critique of the Theory of Evolution by Thomas Hunt Morgan

As the researchers discovered, X-chromosome inactivation can lead to autoimmune disorders, but other factors can also cause these disorders -- which is why men sometimes develop them.

From Science Daily ● Feb. 1, 2024

Performing that so-called X-chromosome inactivation is a special type of RNA called Xist, pronounced like “exist.”

From Seattle Times ● Feb. 1, 2024

His team is studying the handful of X-chromosome genes now known to be more active in females than in males.

From Nature ● Feb. 17, 2015

The ABC bears, as they’re called, look outwardly like brown bears, but their mitochondrial DNA comes from polar bears, as does a portion of their X-chromosome.

From New York Times ● Aug. 14, 2014

But among the males, the odd chromosome, also known as the X-chromosome, can perforce go only into half of the sperm cells, leaving the others without it.

From The Glands Regulating Personality by Louis Berman M.D.