Fetal sex can be diagnosed by noting the presence or absence of the Barr body in cells obtained from the amniotic fluid. What is the etiology of the Barr body?
The Barr body is formed from inactivation of one X chromosome in a female. The female has evolved a mechanism for permanent inactivation of one of the X chromosomes presumably because a double dose of X chromosome products would be lethal.
Inactivation of both X chromosomes
Inactivation of homologous chromosomes
Inactivation of one Y chromosome
Inactivation of one X chromosome
General Embryology 2