Question

Barr Body represents
A) Heterochromatin in male and female cells.
B) All heterochromatic in female cells.
C) One of the two X-chromosomes in the somatic cells of females.
D) Y-chromosome in the somatic cells.

Answer 1

All of the females (mammals) have two X chromosomes. One out of the two X-chromosomes is inactivated by Lyonization. This inactive X chromosome is called - Barr body.

Complete answer:

Option a) : Heterochromatin and Euchromatin are the 2 major categories of chromatin’s structure. Heterochromatin is a tightly packed (and a highly dense) form of DNA.
It is so compactly organized that it is inaccessible to the protein involved in gene expression.
Thus, this is an incorrect option.
Option b) : All heterochromatic in female cells - As this statement is incorrect, this option is also incorrect.
Option c) : One of the two X-chromosomes in the somatic cells of females - Out of the two, one X-chromosome is inactivated, so that unnecessary information is not passed onto the next generation. Because the amount of expression of X-chromosome genes should be equal in both males and females. Thus, Barr bodies are very important, to regulate the amount of the X-linked gene products, which get transcribed.Therefore, this is the Correct option.
Option d) : Y-chromosome in somatic cells - In humans, females inherit an X-chromosome from each parent. Whereas, males always inherit their X-chromosome from their mother and their Y-chromosome from their father. All of the somatic cells in human males contain both, one X and one Y chromosome.
Thus, this is an incorrect option.

Hence the correct answer is option ‘C’.

Note: The process of the X(chromosome)-inactivation was discovered by Mary F. Lyon, who was a British geneticist.

Inactivation of any one of the X-chromosomes in females, is random. It occurs during the embryo development.
This inactive X-chromosome remains inactive in all the future generations of that cell.