X Chromosome Fact Sheet
The X chromosome determines your sex, gives some females super color vision and lends its magic to a certain breed of cat.

10 Neat Facts About the X Chromosome
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In the nucleus of each cell, DNA packaged in thread-like structures called chromosomes.
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Most human cells contain 23 pairs of chromosomes. One set of chromosomes comes from the mother, while the other comes from the father. The twenty-third pair is the sex chromosomes, while the rest of the 22 pairs are called autosomes.
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Typically, biologically female individuals have two X chromosomes (XX) while those who are biologically male have one X and one Y chromosome (XY). However, there are exceptions to this rule.
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Biologically female people inherit an X chromosome from their father, and the other X chromosome from their mother. Biologically male people always inherit their X chromosome from their mother.
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The X chromosome is about three times larger than the Y chromosome, containing about 900 genes, while the Y chromosome has about 55 genes.
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Female mammals have two X chromosomes in every cell. However, one of the X chromosomes is inactivated. Such inactivation stops transcription from occurring, hence making sure a potentially toxic double dose of X-linked genes does not occur.
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An inactivated X chromosome gets condensed into a small, dense structure in the nucleus, and is called a Barr body. Barr bodies are commonly used to determine sex.
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Changes in the structure or number of X chromosomes can lead to a number of diseases. For example, trisomy X syndrome is caused by the presence of three X chromosomes instead of two. Turner syndrome occurs when women inherit only one copy of the X chromosome.
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Some women have a rare super color vision trait called tetrachromacy, which is linked to the X chromosome. These women can see up to 100 million shades of color because they have four types of cone cells in their eye instead of the usual three.
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Contrary to popular belief, calico is not a breed of cats, but rather a distinctive coat color pattern linked to the X chromosome. Over 95% of calico cats are female. The patches of fur on a calico cat are orange and black, and the color depends on which X chromosome is inactivated within each patch of color.
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10 Neat Facts About the X Chromosome
-
In the nucleus of each cell, DNA packaged in thread-like structures called chromosomes.
-
Most human cells contain 23 pairs of chromosomes. One set of chromosomes comes from the mother, while the other comes from the father. The twenty-third pair is the sex chromosomes, while the rest of the 22 pairs are called autosomes.
-
Typically, biologically female individuals have two X chromosomes (XX) while those who are biologically male have one X and one Y chromosome (XY). However, there are exceptions to this rule.
-
Biologically female people inherit an X chromosome from their father, and the other X chromosome from their mother. Biologically male people always inherit their X chromosome from their mother.
-
The X chromosome is about three times larger than the Y chromosome, containing about 900 genes, while the Y chromosome has about 55 genes.
-
Female mammals have two X chromosomes in every cell. However, one of the X chromosomes is inactivated. Such inactivation stops transcription from occurring, hence making sure a potentially toxic double dose of X-linked genes does not occur.
-
An inactivated X chromosome gets condensed into a small, dense structure in the nucleus, and is called a Barr body. Barr bodies are commonly used to determine sex.
-
Changes in the structure or number of X chromosomes can lead to a number of diseases. For example, trisomy X syndrome is caused by the presence of three X chromosomes instead of two. Turner syndrome occurs when women inherit only one copy of the X chromosome.
-
Some women have a rare super color vision trait called tetrachromacy, which is linked to the X chromosome. These women can see up to 100 million shades of color because they have four types of cone cells in their eye instead of the usual three.
-
Contrary to popular belief, calico is not a breed of cats, but rather a distinctive coat color pattern linked to the X chromosome. Over 95% of calico cats are female. The patches of fur on a calico cat are orange and black, and the color depends on which X chromosome is inactivated within each patch of color.
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Last updated: August 13, 2020