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Barr Body

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What are Barr Bodies?

MVSAT Dec 2023

The X chromosome is shared by both men and females. Female somatic cells do not participate in sexual reproduction. By lyonization, one of the two X chromosomes is rendered inactive. Barr bodies are the result of an inactive X chromosome.

X-inactivation Method

Mary F. Lyon, a British geneticist, discovered the X-inactivation method. One X-chromosome is deactivated to prevent unwanted information from being handed down to future generations. Both males and females should have the same quantity of X-chromosome gene expression. The active X-chromosome is surrounded by euchromatin, whereas the inactive X-chromosome is surrounded by heterochromatin. The dormant X-chromosome is compressed, making it inaccessible to transcription molecules. The X chromosome is compressed to form a tiny, dense structure termed Barr body during X-inactivation.

Formation of Barr Body

Any chromosome can be inactivated at any time, and that chromosome will stay inactive for the rest of the cell's life. As a result, in each cell, there is only one active X chromosome. When compared to the total number of X chromosomes, the number of Barr bodies is always one unit lower. It's crucial to consider mutation while trying to figure out what a Barr body is. Barr's body will still be smaller than X chromosomes even if an extra X chromosome is inserted, as in Klinefelter syndrome in men.

Functions of Barr Body

The importance of the Barr body can be considered in terms of its efficacy in detecting physiological abnormalities. Barr body is found in the lobes of neutrophils in female cells. This type of detection is critical for reporting any abnormalities.

Lyon’s Hypothesis

The following are the postulates of Lyon's hypothesis:

  • In female mammals, one of the two X-chromosomes in the somatic cell is inactive.

  • Inactivation of the X-chromosome occurs at random.

  • During development, the inactivation takes place.

  • The dormant X chromosome stays inactive throughout the cell's generations.

Barr Body and X-inactivation Example

During embryonic development, a female cat with black and tan colour alleles on the X chromosome inactivates her two Xs. The result is a coat pattern in the form of a tortoiseshell with black and brown fur patches that alternate. The black spots come from an active black allele on the X-chromosome, whereas the tan patches come from an active tan allele on the X-chromosome.

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FAQs on Barr Body

1. What is the definition of Barr Body?

Barr body is defined as a highly stained inactivated condensed X chromosome found in every somatic cell of most female animals and used as a genetic femaleness test. It is also known as sex chromatin. The term Barr body was first used in 1961. The etymological meaning of Barr body was provided by Murray Llewellyn Barr.

2. Why do males have no Barr Body?

Barr Bodies are X chromosomes that have been compressed and inactivated and are found only in female animals. Barr Bodies can be discovered in hair, buccal cells, and blood, among other biological materials. Because women have two X chromosomes, one of which is inactive, a single Barr Body is present in female mammalian cells, but males have only one X chromosome and hence no Barr Body.

3. What does a Barr body do?

Barr bodies are needed to control how much X-linked gene product is transcribed. One of the X chromosomes in a female becomes highly condensed - the Barr body - to guarantee that X-linked gene product dosages are kept consistent between men and females. As a result, proteins that drive gene transcription are unable to access genetic information on the chromosome. Dosage compensation is the term for this.

4. Is the Barr Body normal?

In a normal female somatic cell, the Barr body is an inactive X chromosome. Lyonization is the process of inactivating these chromosomes. Lyonization is important in both genetics and medicine. Barr's body is clearly identifiable using common stains. When utilized correctly, it can also assist in determining an individual's sex. The lyonization of Barr's body and its use in sex determination are discussed.

5. Where are Barr Bodies found?

Barr bodies are most typically found on the nucleus' perimeter. Barr bodies, on the other hand, are present in various sections of the nucleus, and many of them are close to a nucleus.

6. Does Vedantu provide study materials for all Chapters in Class 12 Biology?

Yes, Vedantu gives Class 12 Biology study materials. You may get it by clicking on the NCERT Solutions for Class 12 Biology and starting studying for the examinations. The suggested answers are simple to comprehend. The answers are well-explained, and they can be relied upon for exam preparation. The curriculum has been changed, and there is no longer any ambiguity. Students can use the sample papers and essential questions to help them prepare thoroughly. On Vedantu, these solutions are available for free. You may also get these using the Vedantu app or from the Vedantu website.

7. Why is Barr body formed?

Barr body is formed when an X chromosome is compacted into a dense and small body where the genes remain inactivated. 

  1. Barr bodies are typically found in _______________

Ans. Female somatic cells 

  1. If a female's cells have three chromosomes, then what is the number of Barr bodies in each cell?

Ans. Two

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