Take the 2-minute tour ×  When identical twins marry identical
twins, the children of the couples will be full genetic siblings
but why are they not genetically identical?  share|improve this
question I think we need more information. What is the evidence
for your assertion? –  kmm Oct 5 '12 at 2:54 Apparently this
phenomenon (twins marrying twins) is called "quaternary
marriage." Useful to know because (1) you can change the title
of your question to be more precise (and maybe get better
answers to your question); and (2) you now have a starting point
to dig around to find answers. –  Steve Lianoglou Oct 5 '12 at
3:16  1 Answer 1  They are not identical for the same reason
full siblings are not identical.  A simplistic Mendelian setup
would be the following:  X1/X2 = Mothers X3/Y = Fathers  That
means the children could be:   So children born to two married
couples composed of identical twins only have a 50/50 shot at
being the same gender, much less have the exact same set of
genes and express them in the s