Question

One Barr body is found in the man of genotype
A. XY
B. XXXY
C. XXY
D. XX

Answer 1

Hint: The Barr body also called the sex chromatin is the inactive and condensed X chromosome found in organisms having XY type of sex determination. This X chromosome is inactivated by the process called Lyonization.

Complete answer:
A Human being having the XY type of sex determination has 23 pairs of chromosomes in which 22 pairs of chromosomes are autosomes or body chromosomes that are similar in all organisms. The last pair of chromosomes is the allosomes or the sex chromosomes that differ in males and females and are responsible for the sex of an individual. The sex chromosomes in males are XY whereas, in females it is XX. To equalize the phenotype of X chromosomes in males and females, one of the X chromosomes in the female is inactivated and called the Barr body. The number of Barr bodies or inactivated X chromosomes is determined by subtracting 1 from the total number of X chromosomes. In females, who carry one X chromosome extra than males, the other X chromosome is inactivated, condensed, and shut down in the heterochromatin- a transcriptionally inactive structure.

This phenomenon is a result of the process called dosage compensation that balances the expression of X-linked genes between males and females.
In males that have more than one X chromosome, the extra X chromosome is inactivated and the number of Barr bodies in that individual will be 1 less than the total number of X chromosomes.

Let us analyze the options one by one to find the correct answer.

Option A: In XY since there is only one X chromosome, the number of barr bodies in this individual will be zero. Therefore, this is an incorrect option.

Option B: XXXY, the total number of barr bodies in this individual will be one less than the total number of X chromosomes, i.e, 2. Therefore, this is an incorrect option.
Option C: XXY, depicts the condition of Klinefelter syndromes in men where the number of Barr bodies in an individual is 1. Therefore, this is the correct option.

Option D: XX, the number of Barr bodies in this individual is 1, but this pair of sex chromosomes are present in females and not males. Therefore, this is an incorrect option.

Hence, the correct answer is option (C)

Note: Klinefelter syndrome is a genetic condition that occurs in males who have XXY pair of sex chromosomes, i.e, an extra copy of the X chromosome. These individuals produce a lesser amount of testosterone which results in lesser body and facial hair, muscle mass, and development of certain feminine characters. They produce less or no sperms and thus are mostly infertile.