Number of Barr bodies in XXY males is?
ANSWER: (A) 1REF: Robbins 8th ed chapter 5Before you understand barr bodies one must understand the principle of Lyon s hypothesisLyons hypothesis:Only one of the X chromosomes is genetically activeThe other X of either maternal or paternal origin undergoes heteropyknosis and is rendered inactiveInactivation of either the maternal or paternal X occurs at random among all the cells of the blastocyst on or about day 16 of embryonic lifeInactivation of the same X chromosome persists in all the cells derived from each precursor cellThe molecular basis of X inactivation involves a unique gene called XISTThe inactive X can be seen in the interphase nucleus as a darkly staining small mass in contact with the nuclear membrane known as the Barr body, or X chromatinNo. Of barr bodies is number of X chromosome - 1In XXY male number of Barr bodies= 2-1 = 1
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Genetics