Marmosets are almost always born as fraternal twins that share a common placenta. Cells exchanged during embryonic development make each sibling a "chimera" with a mixture of its own and its sibling's cells. DNA testing recently showed that about half of male marmosets also carry a mixture of sperm cells, so a marmoset baby can actually inherit its uncle's DNA from its own father. "Germ-line Chimerism and Paternal Care in Marmosets (Cllithrix kuhlii)" by C.N. Ross, J.A. French, and G. Orti, Proceedings of the National Academy of Sciences (volume 104), April 10, 2007, pages 6278-6282.

Dave Micklos: Welcome to DNA Today. I’m Dave Micklos… Jan Witkowski: …and I’m Jan Witkowski. We’re here at Cold Spring Harbor Laboratory talking about DNA in the news. DM: And today’s story puts a new spin on the term “I’m a monkey’s uncle.” Now, we use that as an expression of surprise, but some marmoset monkeys who would be surprised to learn they are an uncle to their own offspring. JW: So we’re talking about those cute little monkeys called marmosets. Marmosets almost always give birth to fraternal twins, and it has been known since the 1960s that these twins are patchworks of their own cells – they are chimeras. This occurs because the placentas of the twins fuse, so there is a channel, a passageway, by which cells from one twin can migrate into another twin. DM: Yes, so these marmosets are a bit like the mythical chimera, which was part goat, part serpent and part lion. Recently at the University of Nebraska, they used DNA testing to take a look at these chimeras. That’s the same sort of testing that we use to test in human criminal cases. What they found is that if you look at different cells from one marmoset’s body, some of the DNA is its own and some is like its sibling that was in its womb with it. Now they went even further and they looked at the sperm cells – and lo and behold they found that about half of the marmoset sperm cells might have its own genetic imprint and half might be sperm from the brother. JW: You can guess the rest of the story. The Nebraska team kept careful track of the matings – looking at the DNA in the father’s and the mother’s, and the DNA in the offspring. And they found DNA fingerprints of the uncle, as well as the marmoset that was the father of the offspring. This was an unexpected form of the genetic or hereditary chimeras and most interestingly, this seemed to be reflected in the behaviors of the marmosets. DM: Yes, these marmosets seem to know what’s going on because marmosets recognize their young by smell, many mammals do this. And in fact, the chimeras would have some odor-producing glands that would be from the father, and some would be from the uncle. And what they found was the fathers of these chimeric marmosets spend more time picking them up and carrying them around, than they do of the non-chimeric ones. JW: So here is a bit of sociobiology: it seems that the genetic chimeras are being perceived by their fathers as being more similar to the fathers than the non-chimeric twin. And so the fathers think this chimeric twin is more related to it so cares more for it. DM: It sort of represents a deeper representation of its kin. Now it’s not the same case with the mother, because the mothers handle the chimeric babies less, so I don’t know what you think that means? JW: Well, we shouldn’t pursue that, I don’t think…

marmoset monkeys, germ line, sperm cells, fraternal twins, embryonic development, Dave Micklos, Jan Witkowski