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 the WBC. This indicates that the person under investigation is a

• A. Colour blind
• B. Haemophilic
• C. Normal female
• D. Normal male
• E. Diabetic

Answer 1

The correct option is C Normal female

As we know that human females have two copies of X-chromosome while male has only single copy. To compensate the dosage of X-linked genes in human male and female, one X-chromosome in females is deactivated and is present as darkly stained body near nuclear envelop. The number of Barr bodies is always one less than the total number of X chromosomes. A human male with XY sex chromosomes lack Barr body which makes option D wrong. A normal human female with XX sex chromosome has 1 Barr body; option C is correct. Both haemophilia and colour blindness are X-linked recessive disorders; a female needs two copies of the affected allele to express the disease which means that a haemophilic or colour blind woman has two active X-chromosomes and no Barr body; options A and B are incorrect. Diabetes is caused by hormonal imbalance and does not have any correlation with number of X–chromosomes; option E is incorrect. Correct answer is C.