Barr body
A Barr body is an inactivated, condensed X chromosome found in the cells of female mammals. This phenomenon occurs during embryonic development when one of the two X chromosomes in a female embryo is deactivated to prevent the unnecessary doubling of genetic material. This process, known as lyonization, ensures that females, who possess two X chromosomes, do not experience an imbalance in genetic information that could arise if both X chromosomes were active. The term "Barr body" is named after Canadian medical researcher Murray Barr, who, along with his assistant Ewart Bertram, first identified these structures in 1948 while studying the effects of stress on the nervous system in cats. Their research revealed that these dark-staining bodies were present solely in female cells. Barr bodies are significant in understanding genetic inheritance and the mechanisms by which sex chromosomes operate in different genders. Consequently, the presence of Barr bodies is a critical aspect of genetics that highlights the intricate processes of cellular function and human development.
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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 passing down unnecessary genetic material to their offspring. 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 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. The deactivated chromosome contains identical genes to the active one, but it becomes condensed so it cannot be used to pass on genetic information. 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 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 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 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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