Learn why identical twins are almost always the same sex, though they may be different genders. Although there are some rare exceptions, identical twins are almost always the same sex. Because ...

Identical twins are not as identical as previously assumed ... The new study focuses specifically on mutations that occur as or before embryos form from the mass ...

MZ twins are generally assumed to be genetically identical, although some genetic and epigenetic differences have now been described. A newly published finding that phenotypically concordant as ...