Question

How many inactivated hetero-chromatinised X-chromosome are present in 44+XXX female?
A. 4
B. 3
C. 2
D. 1

Answer 1

Hint: The inactivated X chromosomes can be counted easily and determined as it is always present one lesser in number than the total number of X chromosomes that is subtract one from the total number of X chromosomes.

Complete answer:
X-inactivation is the process where one copy of the X chromosome of a female is not activated. It is inactivated as it has a transcriptionally inactive heterochromatin. During the crossing of gene expression the output of X-inactivation is that all normal females are mosaics to this chromosome. So a barr body is an inactive X chromosome in a cell with more than one X chromosome which is not active and is known as lyonization. It is discovered by Murray Bar.
It states that in the cell with multiple X chromosomes, one is inactivated during the time of mammalian embryogenesis. This happens in some extra-embryonic tissues of placental mammals. But in the case of human beings it is inactivated either from male or female. So after zygote if it is male then no bar body if female then one barr body.
The bar body consists of an inactivated X chromosome in a cell with more than one X chromosome. The female with two X chromosomes has one barr body. For example- females chromosomes are XX therefore they have one bar body whereas someone with one X chromosome has no barr body, for example males have XY chromosome so there are no barr bodies in males. The barr body is calculated as one less than the total number of X chromosomes present. If we calculate the bar body in females which have XX chromosomes the bar body will be one.
In the question of the bar body of XXX female is asked which means that female has three chromosomes therefore the bar body will be one less than the total number of chromosomes present. The total number of chromosomes are three so the bar body will be two as one can express and two will not be active.

Hence, the correct answer is option (C).

Note: The barr bodies are regarded as diagnostic of genetic femaleness. The inactive chromosome can be seen under the microscope which is seen as a shapeless, dark stained bar body.