Barr body

A Barr body is an inactivated, condensed X chromosome found in female mammal cells. A chromosome is a strand of genetic material passed down from parents to their offspring. During embryonic development, female embryos deactivate one of their two X chromosomes to avoid having double the gene products. These deactivated chromosomes are called Barr bodies, after Canadian medical researcher Murray Barr, who discovered their existence in 1948.

Overview

A chromosome is a thread-like DNA molecule that carries genetic information and is found in a cell’s nucleus. The DNA provides the genetic instructions for the cells, telling them how to function, grow, or reproduce. Chromosomes contain genetic information that is passed down from the mother and father to their children. Humans have twenty-three pairs of chromosomes, twenty-two pairs of which are the same in both males and females. These twenty-two chromosome pairs contain genes that are responsible for hereditary traits such as eye color, height, and facial features.

The twenty-third pair of chromosomes is responsible for determining sex. Females have two X chromosomes in their genes, while males have an X and a Y chromosome. Each parent passes down one chromosome in each pair during fertilization, so that children receive half their chromosomes from their father’s sperm and half from their mother’s egg. The mother always passes down one of her X chromosomes to her children, while the father can pass down either an X or a Y. If he passes down a Y, then their child will be biologically male; if he passes down an X, then she will be biologically female.

If the father passes down an X chromosome, the female offspring’s unused X chromosome becomes unnecessary and is deactivated. However, the deactivated chromosome is homologous to the active one. If both X chromosomes were activated, then the child would have an imbalance of genetic material. The X chromosome that is deactivated will remain that way for the life of the cell.

X chromosomes contain a gene that produces ribonucleic acid (RNA) that deactivates the chromosome. They also contain another gene that regulates the process and resists deactivation. When one X chromosome is used by the cell, the other increases the amount of deactivation of RNA, and the chromosome condenses and is “switched off.” The deactivation process is called lyonization, which was named after its discoverer, British geneticist Mary Lyon.

The deactivated X chromosome is called a Barr body. It was first observed in 1948 by Canadian geneticist Murray Barr and his assistant Ewart Bertram. Barr and Bertram were researching how stress affected the nervous system. They were examining the cells of cats when they noticed a dark-colored body in the cell nuclei of some cats during staining tests. Further research revealed that these bodies were only present in the cells of female cats. Barr and Bertram also identified the bodies in the cells of human females and later identified them as deactivated X chromosomes. They published their findings on the subject in 1949.

Bibliography

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