Table of Contents
- What is a Barr Body?
- Formation of Barr Bodies
- Lyon’s Hypothesis
- What is the function of Barr Body?
- X-Inactivation Example and Barr Body
What is a Barr Body?
“Barr body is the inactive X-chromosome in the somatic cells of mammalian females.”
Females have two X chromosomes. Since the somatic cells of females are not involved in sexual reproduction. Here one of the two X chromosomes is inactivated by lyonization. This inactive X chromosome is known as a Barr body.
The process of X-inactivation was discovered by Mary F. Lyon, a British geneticist. One X-chromosome is inactivated so that unnecessary information is not passed on to the next generation. The amount of expression of X-chromosome genes should be equal in both males and females.
The active X-chromosome is enclosed within euchromatin, whereas, the inactive X-chromosome is enclosed within heterochromatin. The inactive X-chromosome is compacted and is not accessible to the molecules involved in transcription.
In X-inactivation, the X chromosome is compacted to create a small, dense structure called the Barr body.
Also Read: Genetics
Formation of Barr Bodies
The X-chromosomes have an X-inactivation centre (XIC) which contains a gene called X-inactive specific transcript (Xist). There is yet another gene known as Tsix (Xist reversed).
Xist is responsible for the inactivation of the X-chromosome, whereas Tsix prevents it. X-inactivation is a random process that occurs during embryo development.
Lyon’s hypothesis states the following postulates:
- In female mammals, one of the two X-chromosomes in the somatic cell is inactive.
- The inactivation of the X-chromosome is random.
- The inactivation occurs during development.
- The inactive X chromosome remains inactivated in all the generations of the cell.
What is the function of the Barr Body?
The female possesses two X chromosomes compared to one X chromosome in males. Hence, to regulate the number of gene products of genes present on the X chromosome, one of the X-chromosomes becomes inactive in females.
X-Inactivation Example and Barr Body
If a female cat has black and tan colour alleles on the X chromosome, it inactivates its two Xs during embryonic development. This results in a tortoiseshell coat pattern containing alternate patches of black and tan fur. The black patches are obtained from the X-chromosome with an active black allele, whereas, the tan patches are obtained from the X-chromosome with an active tan allele.
Also Read: Sex Determination
For more information on Barr bodies and related topics, keep visiting BYJU’S website or download BYJU’S app for further reference.