Can a boy and girl be scientificaly(sp?) indentical twins?

technically all twins are either mono zygotic which is one egg and usually called identical but this is not always true and then there are dizygotic which is what is usually called fraternal. It is rare but possible for mono zygotic twins to be boy/girl therefore they would not be identical. This can happen when an XY egg splits and one portion is XY (normal boy) and the other ends up just X which would be a girl but with problems. Also there can be an XXY egg which splits in to XY (boy) and XX (girl).