There was an episode of Radio Lab that featured a woman who is a chimera. she was having her dna tested (blood) for something and it was discovered that she isn't the mother of her children. they checked again. the father matched, but not her. then they checked her dna elsewhere (skin, different organs etc.) and found out that she was two people. some parts of her body were one, some parts were another. it's like she's a siamese twin joined at the everything. the twin that has the blood is different than the twin that made the eggs her kids were born from, so they didn't match.
pretty damn weird.