Table of Contents
What are Barr Bodies?
Barr Body Definition:
Barr bodies are condensed, inactive X chromosomes that are found in the nucleus of female cells. They named after the scientist who first discovered them, Murray Barr. Barr bodies not found in the nucleus of male cells.
X-inactivation Method
The x-inactivation method is a technique used to determine the sex of an individual. The method is based on the fact that females have two X chromosomes, while males have only one. The x-inactivation method involves counting the number of Barr bodies in a cell. Barr bodies are dense regions in the nucleus of a female cell that caused by the inactivation of one of the X chromosomes. If a cell has one Barr body, it is likely that the individual is male. If a cell has two Barr bodies, it is likely that the individual is female.
Formation of Barr Body
- A Barr body (named after its discoverer, Murray Barr) is a condensed, inactive X chromosome found in the nucleus of female somatic cells. It is a darkly stain, roughly cylindrical body about 1.5 micrometres in diameter.
- The Barr body formed early in female development, when the X chromosome in the embryo’s cells becomes inactive. The inactive X chromosome condensed and becomes the Barr body. The Barr body remains in the cell’s nucleus throughout the woman’s life.
- The Barr body not found in the nucleus of male cells, because the Y chromosome is not inactive.
Functions of Barr Body
- The Barr body is a structure that found in the nucleus of a female cell.
- This body named after its discoverer, Maurice Barr. The Barr body is a condensed, inactive X chromosome.
- This chromosome only found in female cells, as it is the X chromosome that is not active in males.
- The Barr body helps to ensure that the female cells only express the genes that found on the active X chromosome.
Lyon’s Hypothesis
Lyon’s hypothesis is that the X chromosome inactivation process that ensures that female mammals only have one X chromosome active in each cell, is random. This means that the X chromosome that inactivated in a particular cell is not necessarily the same one that was inactivated in the cell before it.
Barr Body and X-inactivation Example
- A Barr body is a condensed, inactive X chromosome in a female somatic cell. It named after its discoverer, Murray Barr.
- X-inactivation is a process of gene silencing that occurs in female mammals. One of the two X chromosomes in a female cell inactivated early in development. This process ensures that only one X chromosome is active in each cell, which is necessary because many genes on the X chromosome are harmful to a female embryo.
