This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics, Subject name: Pathology
[{'content': "With reference to females, Lyon's hypothesis refers to: \nSelect and explain. \nA. Inactivation of Y chromosome, B. Random inactivation of one of the X-chromosome through heterochromatism, C. Activation of X chromosome, D. All of the above", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. b (Random inactivation of one of X-chromosome through heterochromatism). (Ref. Robbin\'s patho-7th/178)Lyon outlined the X-inactivation, what is Lyonization commonly known as Lyon hypothesis occurs about 16th day of embryonic life. Female carriers of X- linked recessive disorders rarely affected because of random inactivation of X chromosomes in each cell.LYON\'S HYPOTHESIS# "In all cells of females, one X-chromosomes is made transcriptionally inactive through heterochromatism".# It occurs on 16th day of gestation.(Q)# The inactive X can be seen in the interphase nucleus as a darkly staining small mass in contact with the nucleai membrane known as the Barr body or X chromatin. (Q)# Barr body is absent in Turners syndrome (XO). (Q)# Male with a barr body is seen in Klinefelter\'s syndrome. (Q)# In female with Klinefelter\'s syndrome, two barr bodies are present.', 'role': 'assistant'}]