Barr Body is an Inactive X Chromosome

The answer is B) inactive. Barr bodies are condensed, inactive X chromosomes that are found in the nuclei of female mammalian cells. They were first observed by Murray Barr and Ewart Bertram in the 1940s and are named after them.

What is a Barr Body?

A Barr body is formed during the process of X chromosome inactivation, which occurs early in embryonic development in female mammals. In mammals, females have two X chromosomes, while males have one X and one Y chromosome. In order to avoid having an overdose of gene products from the X chromosome, one of the X chromosomes in females is randomly inactivated in each cell of the body. This ensures equal gene dosage between males and females.

How is X Chromosome Inactivation Achieved?

X chromosome inactivation is achieved by a process called lyonization. One of the X chromosomes is randomly chosen to become inactivated in each cell. The inactivated X chromosome becomes condensed and forms a heterochromatic structure known as a Barr body. The genes on the Barr body are usually not expressed, resulting in gene silencing.

Appearance and Location of Barr Body

Barr bodies can be visualized using microscopy techniques. They appear as small, darkly stained, drumstick-shaped structures located at the periphery of the nucleus. The number of Barr bodies in a cell corresponds to the number of inactivated X chromosomes.

Function of Barr Bodies

The primary function of Barr bodies is to ensure gene dosage compensation between males and females. By inactivating one of the X chromosomes in females, the same number of active X-linked genes is present as in males. This prevents overexpression of X-linked genes in females.

Reactivation of Barr Bodies

In some cases, certain genes on the Barr body may be reactivated. This can occur during certain stages of development or in specific tissues. However, the majority of genes on the inactivated X chromosome remain silenced throughout the lifespan of the individual.

In conclusion, Barr bodies are inactive X chromosomes that are formed through the process of X chromosome inactivation. They play a crucial role in gene dosage compensation in females by equalizing the expression of X-linked genes with males.