Barr body testing is a test to determine the presence of multiple X chromosomes in a cell. When more than one X chromosome is present in a cell, only one X is allowed to remain active, and any excess X chromosomes are randomly inactivated and condensed. The condensed, inactivated X chromosome is called a Barr Body.
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Barr Body. Transcriptionally dormant X chromosome as found within individuals possessing more than one X chromosome. Such individuals, of course, usually are female but also can be Klinefelter syndrome males.
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Barr body. From Wikipedia, the free encyclopedia. Jump to: navigation, search ... Barr body. In those species in which sex is determined by the presence of the Y or W chromosome rather than the diploid y of the X or Z, a Barr body is the inactive X chromosome in a female cell, or the inactive Z in a male. Barr body Inactivated X-chromosome in mammalian females.
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The reason for the formation of the Barr body is one of dosage compensation, which is to say that most of the genes associated with the X chromosome are expressed to an appropriate extent when found in a single copy, i.e., as one sees in males.
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The cells on the left, taken from a man, do not exhibit any Barr Bodies. The cells on the right, taken from a woman, exhibit one Barr Body per cell. Pros: Barr Body testing was used by both the IOC and the IAAF beginning in 1968.
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Which X chromosome is converted to a Barr body occurs randomly during embryo development and can be a different X chromosome in different tissues. Once converted, the Barr body retains that status through mitotic divisions. Females, as a consequence, are considered to be mosaics with regard to X chromosome inactivation, with some tissues expressing one X chromosome and different tissues the other.
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Each excess X chromosome will form one Barr body. This means that 46,XX women will have cells that exhibit one Barr body, while the cells from a 46, XY male will not exhibit any Barr bodies.
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Meaning and definition of barr body : A dense object lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome. For the term barr body may also exist other definitions and meanings, the meaning and definition indicated above are indicative not be used for medical and legal or special purposes. Source: SFU Text file: http://school.gogpg.com/Portals/1/Assess%20Well/Example%20Sampling%20Domains-Curriculum%20Specific.xls.
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In this method of testing, cells are frozen in interphase, when the Barr body is condensed, and stained to allow viewing under a microscope.
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biology definition of barr body
Barr body is a dense object lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome.