Question

A woman has a child with Klinefelter syndrome. Number of Barr bodies present in the child is
A. One
B. Two
C. Three
D. All of the above

Answer 1

Hint: Klinefelter is a genetic condition affecting males, born with an additional one or more X chromosome. Normally male is heterogametic, having X and Y chromosomes. Due to this, it is sometimes referred to as XXY syndrome.

Complete answer:
Klinefelter syndrome is not an inherited disorder, it occurs due to random genetic error. It comes from both parents equally. The older mother may have slightly increased the chance of a child with Klinefelter syndrome. The patient has 47 or more chromosomes instead of normal 46.

Males born with Klinefelter syndrome may have low testosterone, produce little or no sperm, decreased muscle mass and body and facial hair growth. The klinefelter patient can have 1,2 or 3 Barr bodies depending on the number of X chromosomes present. Its number is always one less than the total number of X chromosomes.

Option A- Barr body or sex chromatin is an inactive X chromosome.
No. Of Barr body = No. Of X chromosomes – 1
Normal male (2A + XY) —> Barr body absent
In Klinefelter syndrome male have an additional X chromosome. Therefore
(2A + XXY) —> 2-1 = One Barr body
Option B- If a child has two extra X chromosomes than Barr bodies present is two.
Option C – If a child has three extra X chromosomes than Barr bodies present are three.
Option D – the patient has 1,2 or 3 Barr bodies depending on the number of X chromosomes present. Its number is always one less than the total number of X chromosomes.

Hence the correct answer is option ‘D’.

Note: Barr body technique also known as Lyon's hypothesis-
The interphase nucleus of human female interphasic two X chromosomes. Out of two, one X chromosome becomes heterochromatin and the other X chromosome is euchromatin. By staining X heterochromatin, it appears as a dense body which is called Barr body.