I used to enjoy watching CSI (the original series), back when Gil Grissom (actor William Petersen) headed that fictional forensics lab. It was never the same after he left.
Anyway, one episode that I still remember involved a crime being committed by someone who was a genetic chimera: someone who had developed from an embryo formed when two fertilised eggs fused together. (There’s a fascinating blog post about chimeras over at damninteresting.com.)The upshot was that some cell lines in that indivdual’s body had one set of DNA, with other cells having a different genetic makeup. In such individuals it’s possible for different tissues to express genes from one or the other lot of DNA, something that’s called mosaicism (it’s also possible in all female mammals, where one or the other X chromosome is randomly inactivated when the embryo is at around the 1000-cell stage of development).
I was reminded of that episode when I saw this photo on Science Alert’s Facebook page (ah, the wonders of modern social networking!):
You’d need to look at the DNA from the white & ‘normal’ sides of this bird to be sure whether what we’re seeing here is definitely the result of a chimera displaying mosaicism. But isn’t it a stunning image?