Turner syndrome occurs when women inherit only one copy of the X chromosome. For example, trisomy X syndrome is caused by the presence of three X chromosomes instead of two. Barr bodies are commonly used to determine sex.Ĭhanges in the structure or number of X chromosomes can lead to a number of diseases. Such inactivation stops transcription from occurring, hence making sure a potentially toxic double dose of X-linked genes does not occur.Īn inactivated X chromosome gets condensed into a small, dense structure in the nucleus, and is called a Barr body.
However, one of the X chromosomes is inactivated. The X chromosome is about three times larger than the Y chromosome, containing about 900 genes, while the Y chromosome has about 55 genes.įemale mammals have two X chromosomes in every cell. Biologically male people always inherit their X chromosome from their mother. However, there are exceptions to this rule.īiologically female people inherit an X chromosome from their father, and the other X chromosome from their mother. Typically, biologically female individuals have two X chromosomes ( XX) while those who are biologically male have one X and one Y chromosome ( XY). The twenty-third pair is the sex chromosomes, while the rest of the 22 pairs are called autosomes. One set of chromosomes comes from the mother, while the other comes from the father.
Most human cells contain 23 pairs of chromosomes. In the nucleus of each cell, DNA packaged in thread-like structures called chromosomes.
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