Question

Where Barr's body is found?

Answer 1

Other name of Barr body is sex chromatin. The inactive X chromosome in a female somatic cell is called Barr Body. This inactive X chromosome condenses into Barr body which lies along the inside of the nuclear envelope. Lyonization is the process of inactivation of these chromosomes. It is both clinically and genetically significant.

Complete Answer:
- An inactive, condensed member of a pair of X chromosomes in a female’s somatic cell is Barr body. It is a small, well defined body which stains intensely with nuclear dyes. It appears as a dense, dark staining spot at the periphery of the nucleus of each somatic cell of a human female.
- It is present in a large proportion of nuclei of female origin. It is absent in male nuclei. The Barr body is found at the periphery of the nucleus. Barr bodies are also found in other parts of the nucleus and many of these are situated in proximity to a nucleolus.
- It was found that 61.8% of Barr bodies were at nuclear periphery, 23.2% were lying against a nucleolus. The size of the Barr body is about 1µ in diameter.Barr bodies have many shapes. Some appear to be plano - convex or wedge shaped. The Barr Body can also be rectangular which is present at the periphery of the nucleus.
- Barr bodies can be identified in cells grown in culture. These bodies can be stained with a large number of nuclear dyes. Common used stains are Cresyl violet, thionin and feulgen.

Note: In men and women, the number of Barr bodies visible at interphase is one less than total number of chromosomes. Women with a 47, XXX karyotype have two Barr bodies. Men with 47, XXY Karyotype have a single Barr body. The Barr body may be seen on the nucleus of neutrophils. Barr bodies are important to regulate the amount of X linked gene product that is being transcribed.