Human Genetics Problem Set

Problem 14 Tutorial: Barr body

A Barr body is:

E. an inactivated X chromosome

Inactivated X chromosome

Females have twice as many copies of the X-chromosomes as males. Do females produce twice as much of the proteins encoded on the X-chromosome? No, because one of the X-chromosomes is condensed into an inactive form in all somatic cells.

The inactive X-chromosome in female somatic cells, visualized as a densely staining body within the nucleus and attached to the nuclear envelope, is known as a "Barr body." Females contain patches of cells in which one or the other X-chromosome has been inactivated, leading to a mosaic pattern of X-chromosome gene expression in different parts of the female body.

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University of Arizona
Revised: November 5, 1998
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