[Biology Class Notes] on Barr Body Pdf

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.