Question

A medical technician while observing a human blood smear under the microscope motes the
presence of the barr body close to the nuclear membrane in the WBC. This indicates that person under
investigation is
1. Colour blind
2. Haemophilic
3. Normal female
4. Normal male

Answer 1

Hint:-White blood cells are the colorless loo corpuscles in mammals like humans. These cells are devoid of haemoglobin and are involved in the immunity reactions of the body. There are five types of WBCs in humans- neutrophils, eosinophils, basophils, lymphocytes and monocytes.

Complete Answer:-
- Humans have 23 pairs of chromosomes, out of which 22 pairs are autosomes and one pair is allosome or sex chromosome. In humans, the females have two X chromosomes while the males have one X and one Y chromosomes as their sex chromosomes.
- So to compensate for this, one of the X chromosomes in females is deactivated and this phenomenon is called dosage compensation.
- This deactivated X-chromosome is present as a darkly stained body near the nuclear envelope and is termed as a barr body.
- The number of barr bodies in an organism can be easily calculated as it is always one less than the total number of X-chromosomes in females.
- So a human female has one barr body as she has two X-chromosomes while a human male has zero barr bodies as he has only X-chromosome.
- Color blindness is a recessive sex-linked defect which occurs due to some mutation in the X-chromosome. In females, the effect of X-linked recessive allele is suppressed by her matching dominant normal gene so it is more common in males than females.
- Haemophila is also a sex-linked recessive trait which is also called bleeder’s disease.
Thus, the right option is 4.

Note:- One of the types of white blood cells is neutrophils that also help in sex differentiation in humans as the neutrophils of females show ‘drum stick’ or ‘barr body’. It represents an inactivated X-chromosome, so also called sex chromatin.