Barr body: the color-staining spot (the sex chromatin) located at the edge of the nucleus of cells taken from individuals with more than one X chromosome. It is normally found in female cells, and so is used as a sign of female genetic sex. It is also found in men with the 47,XXY (Klinefelter's) syndrome. It is missing in girls with the 45,X (Turner's) syndrome. The Barr-body test is rapid and inexpensive as compared with actual chromosome counting, and so is used as a method of preliminary X-chromosome screening.

Dictionary of Sexology Project: Main Index

A Barr body is a condensed, inactive X chromosome found in the somatic (non-gamete) cells of normal females and genetically abnormal males who have more than one X chromosome. Barr bodies are visible when the nucleus of the cell is not dividing.

None of the genes in a Barr body are used, since only one X chromosome can function within a cell. In every cell with more than one X chromosome, one is randomly turned off to create a Barr body. Because of this phenomenon, identical twin girls display more phenotypic differences than identical twin boys.

From the science dictionary at

Log in or register to write something here or to contact authors.