A medical technician while observing a human blood smear under the microscope notes the presence of barr body close to the nuclear membrane in the WBC. This indicates that person under investigation is
A
Colour blind
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B
Haemophilic
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C
Normal female
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D
Normal male
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Solution
The correct option is B Normal female The presence of barr body close to the nuclear membrane in WBC is characteristic of a normal female. The inactivated X-chromosome in the somatic cell of the female is referred to as Barr body which is present as tightly coiled and visible heterochromatin. Dosage compensation in human is accomplished by the inactivation of one of the X chromosomes in females. It occurs in 200 celled embryo wherein each cell independently select either maternal or paternal X chromosome for inactivation. Once the selection is done, all lineages of that cell make the same selection during cell division and tissue differentiation. This random inactivation of materal and paternal X chromosome makes a human female mosaic for X gene.