Barr Body

A Barr body (named after discoverer Murray Barr) is the inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization, in those species in which sex is determined by the presence of the Y (including humans) or W chromosome rather than the diploidy of the X or Z. The Lyon hypothesis states that in cells with multiple X chromosomes, all but one are inactivated during mammalian embryogenesis. This happens early in embryonic development at random in mammals, except in marsupials and in some extra-embryonic tissues of some placental mammals, in which the father's X chromosome is always deactivated.

In men and women with more than one X chromosome, the number of Barr bodies visible at interphase is always one less than the total number of X chromosomes. For example, men with a 47,XXY karyotype have a single Barr body, whereas women with a 47,XXX karyotype have two Barr bodies. Barr bodies can be seen on the nucleus of neutrophils.

Read more about Barr Body:  Mechanism

Famous quotes containing the words barr and/or body:

    Old age is the verdict of life.
    —Amelia E. Barr (1831–1919)

    Belief like any other moving body follows the path of least resistance.
    Samuel Butler (1835–1902)