Barr Body: Difference between revisions
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*In a normal male with the genotype 46XY, the number of Barr bodies would be 0. | *In a normal male with the genotype 46XY, the number of Barr bodies would be 0. | ||
However in a male with [[Klinefelter syndrome|Klinefelter's syndrome]] (where the genotype is 47XXY), the number of Barr bodies would also be 1<ref>Page 262, Hartl D.L and Ruvolo M (2012) Genetics, Analysis of Genes and Genomes, 8th edition, USA: Jones and Bartlett</ref><ref>Alberts, B. Johnnson, A. Lewis, J. Raff, M. Roberts, K and Walter, P. (2008) Molecular Biology of The Cell 5th Edition, New York:Garland Science. (page 473)</ref>. | However in a male with [[Klinefelter syndrome|Klinefelter's syndrome]] (where the genotype is 47XXY), the number of Barr bodies would also be 1 <ref>Page 262, Hartl D.L and Ruvolo M (2012) Genetics, Analysis of Genes and Genomes, 8th edition, USA: Jones and Bartlett</ref><ref>Alberts, B. Johnnson, A. Lewis, J. Raff, M. Roberts, K and Walter, P. (2008) Molecular Biology of The Cell 5th Edition, New York:Garland Science. (page 473)</ref>. | ||
=== Lyonization === | |||
Discovery of barr bodies leads to thousands more question for scientist. The changes that can lead to a permanent impact, is it formed randomly? and are they affecting all cells, or only a selective amount? Thus, [[Mary Lyon|Mary Lyon]] comes with her own ideology to answer these question, and her hypothesis is still accepted till today. | |||
The Lyon Hypothesis: | |||
The Lyon Hypothesis: | |||
*Inactivation is random at an early point in development | |||
*Once inactivated, all progeny cells have the same X-chromosome inactivated<br> | |||
=== Reference === | === Reference === | ||
<references /><br> | <references /><br> | ||
Revision as of 06:56, 25 November 2012
A Barr Body is an inactivated, condensed X chromosome found in female cells.
Since females posses two X chromosomes and males have one X chromosome and a Y chromosomes, Barr bodies are essential to regulate the amount of X-linked gene product being transcribed. To ensure that X-linked gene product doses are kept similar between males and females, one of the X chromosomes in a female becomes very condensed - the Barr body. This results in the genetic information on the chromosome being inaccessible to proteins that cause gene transcription. This is called dosage compensation.
X chromosome Inactivation is random and occurs at an early point of development.
The number of Barr bodies in a cell is one less than the number of X chromosomes. For example:
- In a normal female with the genotype 46XX , the number of Barr bodies would be 1.
- In a normal male with the genotype 46XY, the number of Barr bodies would be 0.
However in a male with Klinefelter's syndrome (where the genotype is 47XXY), the number of Barr bodies would also be 1 [1][2].
Lyonization
Discovery of barr bodies leads to thousands more question for scientist. The changes that can lead to a permanent impact, is it formed randomly? and are they affecting all cells, or only a selective amount? Thus, Mary Lyon comes with her own ideology to answer these question, and her hypothesis is still accepted till today.
The Lyon Hypothesis:
- Inactivation is random at an early point in development
- Once inactivated, all progeny cells have the same X-chromosome inactivated