Question about identical and fraternal twins...?

It isnt possible. Your doctor probably just had a slip of the tongue. Identical twins occurs when one egg is fertilized by one sperm and the embryo splits somewhere in early development- meaning the DNA is the exact same. Fraternal twins is two seperate eggs fertilized by two seperate sperm at or near the same time that just happen to grow together. DNA isnt exactly the same and its possible to have an XY and a XX develop at the same time.