Can Identicals ever be Boy/Girl Twins?
Logically, one would imagine that identical twins by default are the same sex, yet researchers have shown that in some rare cases, identical twins from an egg and sperm which began as male (XY) can actually develop into a male / female pair due to a genetic mishap occuring when the egg divides. This happens when the fertilised egg ‘looses’ one of the copies of the Y chromosome when it is dividing into two embryos in very early development. The resulting babies are then male (XY) and female (XO). The normal genetic make-up of a girl is XX. An XO baby is outwardly a girl, but her cells only have one copy of the X chromosome, not two. This condition is called Turner Syndrome.
