Question

A medical technician while observing a human blood smear under the microscope notes the presence of a Barr body close to the nuclear membrane in WBC. This indicates that the person under investigation is
A. Colorblind
B. Haemophilic
C. Normal female
D. Normal male
E. Diabetic

Answer 1

Hint:- Barr body is an inactive X chromosome present in the cell. The cells containing multiple X chromosomes have one inactivated X chromosome. They get inactivated during mammalian embryogenesis. In humans, the presence of more than one X chromosome then the number of Barr bodies present is always one less than the total X chromosomes.

Complete answer:
To compensate for the dosage of the X chromosome in the cell one chromosome gets inactivated during embryogenesis. In males, there is only one X chromosome which indicates that no Barr body is present in the male.
In females, there is the presence of two X chromosomes so in females one, X chromosome gets inactivated and one is present as Barr body. So in the blood smear given in the question, we can say that female blood is under observation.
A person who has diabetes has no relation with the presence or absence of the barr body as diabetes is caused due to hormonal imbalance in the body and it is not a sex-linked disease.
Haemophilia and colorblindness are X-linked recessive diseases that are caused when a female is infected. And for that female needs two affected alleles to express the disease. Such women have only no barr body as both the X chromosomes are active.
So the answer is option (C), ‘normal female’.

Note:-
Dosage compensation is the process in which organisms try to equalize the expression of genes. Such is the case with the Barr body which is used to compensate for the expression of X chromosome in a cell. In Klinefelter males, the barr bodies present in them are one, and females having XXX chromosomes have two barr bodies.