Question

Number of Barr bodies in XXXXY is
A) 1
B) 2
C) 3
D) 4

Answer 1

In females, two X chromosomes are present and one of the X chromosomes is inactivated. The inactivated X chromosome is known as Barr body.

Complete answer:
Barr's body was first demonstrated by MF Lyon who was a british geneticist. The process of inactivation of one X chromosome happens so as to avoid passing of unnecessary information to the next generation. Lynon had made a hypothesis, and following are its postulates,

The inactivation of X chromosome happens in random
The inactivation of X chromosome occurs during the development
The inactive X chromosome is alway inactivated across all generation of cells
In female, only one of two X-chromosomes in the somatic cell is inactive

As we know, only one X is always active, thus, in XXXXY, three X are degenerated. Therefore, there are three Barr bodies present in XXXXY. Thus, this is the correct option.

Additional information : Formation of Barr bodies
i) The X-chromosomes have a center which is known as X-inactivation center (XIC) which contains a gene known as X-inactive specific transcript (Xist)
ii) Xist is generally responsible for the inactivation of X-chromosome whereas another genes known as Tsix is known to reverse it

Hence the correct answer is option ‘C’/

Note: The number of Barr bodies present are different in different cases,
i) Humans - No Barr bodies
ii) Turner’s syndrome - No Barr bodies
iii) XXXfemale and XXXY and XXXYY male - 2 Barr bodies
iv) XXXXY male - 3 Barr bodies