<prompt> With reference to females, Lyons hypothesis refers to:Inactivation of Y chromosomeRandom inactivation of one of the X-chromosome through heterochromatismActivation of X chromosomeAll of the above  <response>: Ans. b Random inactivation of one of X-chromosome through heterochromatism. Ref. Robbins patho-7th178Lyon 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.LYONS 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 Klinefelters syndrome. Q In female with Klinefelters syndrome, two barr bodies are present. 