Was it mentioned? I didn't notice if so.. Cause in real surrogacy two can make it to the egg that's why most same sex couples that wanted a child of their own went for surrogacy.
You could add two sperm to an egg in which you have removed the DNA. You'd end up with a child with just a bit of the donor's DNA but the fertilized egg would have the DNA of both parents.
I feel so bad for Yi yun..it makes me wanna kill a Bitch with a pink hair ㅠㅠ