X inactivation is not imprinted in human extra-embryonic tissues (see
Migeon BR et al 2001).
Investigation of methylation of the androgen receptor gene using digestion of the X chromosome DNA
with the methylation-sensitive restriction enzyme, Hpall, followed by PCR amplification showed that
the paternal allele was preferentially methylated in trophoblastic cells, but not in mesodermal
cells of human chorionic villous, suggesting that the paternal X chromosome is preferentially
inactivated in the human extra-embryonic tissues early in development (Goto
T et al 1997). Extraembryonic tissues in mice show Xist and X chromosome imprinting (Takagi
N and Sasaki M 1975).