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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

They also generally have a more active immune response, partly due to genetic factors like the X chromosome.

From Science Daily • Apr. 13, 2026

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

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

This tallies with the fact that the gene is carried on the X chromosome.

From BBC • May 15, 2025

The sex is thus determined by the male gamete, the X chromosome united with that of the female gamete producing female individuals, while the Y united with X produces male individuals.

From Hormones and Heredity by Cunningham, J. T.