Utsikt
Senior Member (Voting Rights)
There are very rare exceptions:I was wandering about the obvious things such a different sex twins (or more), something most people will have come across in their lives, which per definition cannot be identical.

Monozygotic twins of opposite sex - PubMed
Although discordant karyotypes are known in identical twins, cases involving differences in sex phenotype are rare. We studied identical twins with the 46,XY karyotype - a male with mixed gonadal dysgenesis and a female with "pure" gonadal dysgenesis. The testis-determining SRY gene was present...
