Tuesday, September 17, 2013

Biologically speaking, what is an individual, pray tell?

The New York Times published a fascinating article yesterday, DNA Double Take, by Carl Zimmer, that calls into question the nearly universal belief that every cell in an individual's body contains the same DNA-- the DNA determining an individual's biological identity. This now appears to be a gross oversimplification.
Carrying more than one type of DNA is called "chimerism." It was previously considered rare, since evidence for it only occasionally thrust itself into visibility. Now that sequencing the human genome has become much less expensive to do, chimerism is becoming more visible. These weren't previously unknown-- Zimmer notes that in 1953, when a woman donated a pint of blood, some of which was Type O and some Type A, it was concluded that she'd acquired some of her blood from her twin brother, while in the womb. But now, scientists have begun to search systematically for chimeras-- and are finding that chimerism is not at all rare, and in fact occurs
Besides the implications for medicine, the discovery of the prevalence of chimerism is likely to complicate forensic science. Zimmer cites a case that arose last year, in which a saliva sample and sperm sample from the same suspect in a sexual assault case didn't match because the suspect had two sequences of DNA in his body.

I see the discovery of the prevalence of chimerism as further undermining the common, even cherished conception of the genome as a master blueprint that allows everyone to be neatly pigeonholed and offers the means for tinkering with and easily controlling desirable traits once the practical issues of genetic engineering have been worked out-- and, of course, bolsters the illusions people have about the biology of sex differences. Some people, of course, will be certain that acquiring neurons with Y-chromosomes will make a significant difference to the operation of women's brains following the birth of sons. I imagine there may even be a few neuroscientists willing to squander grant money in attempt to locate and prove such a difference. But such old, cliche-ridden projects will inevitably begin to look less and less interesting. Just the other day I read an article in Science reporting that the hottest, fastest-moving research of the day is on bacterial immune systems (and to tell the truth, until I read that article I hadn't even known bacteria have immune systems!)-- and that bacterial immune systems are being used to harness features to target the destruction of specific genes in human cells. Nothing about human biology is as simple as it once seemed. And I say: Glory hallelujah!


Therem said...

Wow, this is blowing my mind even as I type this! Thanks so much for posting this!

Vandana Singh said...

This is beyond cool! thanks, Timmi!