The really weird part of this article:
Women accidentally carrying a “twin’s” child
Lydia Fairchild’s paternity test was meant to be straightforward, proving to the courts that her two sons’ father was the person she said he was. When the test came back, however, Fairchild herself came up as a blank: there was no trace of her DNA in her own children.
The courts threatened to convict her of illegal surrogacy – they assumed it was a scam to gain benefits. Luckily, at around the same time, a scientific paper reported a similar case in which a woman was apparently not the biological mother of two of her three children. The reason was that she was a chimera: a case in which two twins had merged into one body early in development. Being the product of two different cell lines, some of her eggs carried a genome that was different from the rest of the body.
Needless to say, the discovery has caused Fairchild to question her own identity. “Telling my sons about this was the hardest part because I felt that part of me hadn’t passed on to them,” she told the website Jezebel. “I thought, ‘Oh, I wonder if they’ll really feel that I’m not quite their real mother somehow because the genes that I should’ve given to them, I didn’t give to them.’”
The article mentions that you can actually be a chimera with cells from a living twin too, and that happens with 8% of non-identical twins and 21% of triplets - so theoretically your living sister could be the genetic mother of your child.
