With reference to females, Lyon's hypothesis refers to:

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.