Why can twins resulting from a single fertilized egg,

Question

Why can twins resulting from a single fertilized egg exchange blood or receive organ transplant from each other without rejection, while twins resulting from two fertilized eggs sometimes cannot

Answer 1

Twins from a single fertilized egg are called "identical" twins and share the same DNA.

Twins from 2 fertilized eggs are called "fraternal twins" and are no more similar to each other than any 2 offspring of the same parents.

Answer 2

Twins resulting from a single fertilized egg have exactly the same DNA.  Therefore, the antigens on their cells will be the same and their immune system will recognize the other twin's organs as their own.

However, twins from two different eggs are not identical.  They have different genes from mom and dad (two different sperm were involved).  It's the same as regular siblings, only they were conceived at th same time.  Because their DNA is not identical, the antigens on their cells will be different their immune system would react against the other twins organs.  However, just like with regular siblings, sometimes the genes for antigens can be similar enough to allow for transplants.

Answer 3

same egg, they are called identical twins, so all of their DNA is exactly the same, is it is almost like taking from self and giving back to self.

the other type is called un-identical twins are from two different   sperm and egg that happed to be fertilized at same time; their genetic info is different. there might be problem specially if donating blood.