Question

In the cell of superfemale with 47 chromosomes (44+XXX) visible Barr bodies are –
A. 1
B. 0
C. 2
D. 3

Answer 1

Hint: The number of visible Barr bodies can be counted easily as it is always present one lesser in number than the total number of X chromosomes.

Complete answer
A Barr body is an inactive X chromosome present in a cell where the X chromosomes are more than one. The number of Barr bodies in humans is always found to be one lesser than the tidal number of X chromosomes which is visible at the interphase and when the X chromosome present is more than one.

Additional information
- A Barr body is named after it’s discoverer Murray Barr.
- Barr body is an inactive form of chromosome in a process called lyonization, during XY sex determination.
- According to the Lyon hypothesis, the cells with multiple X chromosomes will have one inactivated X chromosome during the process of mammalian embryogenesis.
- This anomaly occurs during the early stage of embryogenesis.
- It occurs in almost all the mammals except some placental mammals where the X chromosome of the sperm is generally inactivated.
- If a person is suffering from Klinefelter syndrome having 47+XXY chromosomes then Barr’s body will be one less than the X chromosome which will be one.
- If a person is having a karyotype 47+XXX chromosomes, then the Barr bodies present will be two.
So, the correct answer is ‘2’.

Note: A person with two X chromosomes as in the case of human females has only one Barr body while the person with one X chromosome as in the case of human males will have no Barr body. Barr bodies can be seen in the nucleus of the neutrophils, at the corner of the nucleus in female somatic cells between divisions. The Barr body is responsible for femaleness genetically.