Twin Family

Contrary to common opinion, identical twins are not always of the same phenotypical sex. There have been described cases where monozygocity resulted in 46,XO (i.e. female with Turner syndrome) and 46,XY (i.e. male). This is thought to be due to unequal distribution of zygotic protoplasm. However, as a rule, traits and physical appearances of MZ twins are very similar.
Identical twins look alike, although they do not have the same fingerprints (which are environmental as well as genetic). As they mature, identical twins often become less alike or more alike because of lifestyle choices or external influences. The children of identical twins would test genetically as half-siblings rather than first cousins.