Sex chromosones

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The sex chromosomes play a highly specialized role in germ cell development in mammals, being enriched in genes expressed in the testis and ovary. Sex chromosome abnormalities e. Understanding how sex-gene expression is regulated is therefore critical to our understanding of human reproduction. Here, we describe how the expression of sex-linked genes varies during germ cell development; in females, the inactive X chromosome is reactivated before meiosis, whereas in males the X and Y chromosomes are inactivated at this stage. We discuss the epigenetics of sex chromosome inactivation and how this process has influenced the gene content of the mammalian X and Y chromosomes.
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Function of the Sex Chromosomes in Mammalian Fertility

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Function of the Sex Chromosomes in Mammalian Fertility

Humans are born with 46 chromosomes in 23 pairs. Most women are 46XX and most men are 46XY. Research suggests, however, that in a few births per thousand some individuals will be born with a single sex chromosome 45X or 45Y sex monosomies and some with three or more sex chromosomes 47XXX, 47XYY or 47XXY, etc. In addition, some males are born 46XX due to the translocation of a tiny section of the sex determining region of the Y chromosome.
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Sex chromosome

The nuclei of human cells contain 22 autosomes and 2 sex chromosomes. In females, the sex chromosomes are the 2 X chromosomes. Males have one X chromosome and one Y chromosome. The presence of the Y chromosome is decisive for unleashing the developmental program that leads to a baby boy.
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This page has been archived and is no longer updated. The first inkling that sex chromosomes were unique from all other chromosomes came from experiments conducted by German biologist Hermann Henking in By this point in time, scientists could easily view mitotic cell division using light microscopy.
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