There’s an interesting post up on the New York Times’ Well Blog about children with three biological parents—in this case, three genetic parents. Here, a mother and a father provided chromosomal DNA (i.e., the standard 23 chromosomes from each leading to the diploid 46 chromosomes), and another woman provided the egg, which included DNA found in the mitochondria (the “powerhouses of the cell” which are found in the cytoplasm of the egg). The idea behind this practice is that women with problems in their mitochondria can still have healthy children with their own genetic material. While it’s not that unusual to talk about children with three biological parents (two genetic and one gestational, as happens frequently with a surrogate mother or egg donor), we don’t often think on examples with three genetic parents (and the potential for a fourth biological (gestational)).
As a side note, the technique has an odd history, in that it was used in about 100 babies worldwide in the 1990s, then largely halted by the FDA; efforts are underway to bring it back.
Rather than arguing for or against this particular technique, I want to point out a bit of what it does to our notions of biological parenthood. We’ve already disaggregated parenthood into social and biological, and then biological into gestational and genetic; this is taking another step and separating genetic into chromosomal and mitochondrial. And even the lines we already draw may be a bit fuzzier: epigenetic changes to DNA expression that occur in utero can have lasting impacts on how genes are expressed throughout the life of the infant and beyond, meaning that what we think of as uniquely genetic—biological long-term heritable changes—may be influenced by the gestational mother as well.
A few years ago, I wrote a piece on how the idea of human cloning should make us rethink our understanding of biology as a key aspect of parentage (though I’ve come to rethink my conclusions a bit since then). The Times story helps bring home the point that these questions aren’t somewhere in the distant future; they’re already here.