Question

What is a Barr body, and where is it found in a cell?

Short answer

Answer: A Barr body is an inactivated X chromosome present in the nuclei of female somatic cells. It forms as a result of X-chromosome inactivation during early development to ensure proper gene expression dosage. Barr bodies are found within the cell nucleus, usually attached to the nuclear envelope.

Step-by-step solution

Define Barr Body

A Barr body, also known as a sex chromatin, is an inactivated X chromosome present in the nuclei of female somatic cells. It appears as a dense, compact structure under a microscope, consisting of heterochromatin.

Explain the Formation of Barr Bodies

Barr bodies form during early development as a result of a process called X-chromosome inactivation (XCI). In female mammals, one of the two X chromosomes in each cell is randomly inactivated to ensure the proper dosage of X-linked gene expression in females (XX) and males (XY). The inactive X chromosome condenses into a small, dense structure called a Barr body.

Describe the Location of Barr Bodies

Barr bodies are found within the nucleus of the cell, usually attached to the nuclear envelope. The nuclear envelope is a double-membrane structure that separates the nucleus from the cytoplasm and provides a boundary for the cell's genetic material. Since one X chromosome is inactivated during XCI, only one Barr body is present in most female somatic cells.