Abstract
Since mitochondrial replacement techniques were developed and clinically introduced in the United Kingdom, there has been much discussion of whether these lead to children borne of three parents. In the UK, the regulation of MRT has dealt with this by stipulating that egg donors for the purposes of MRT are not genetic parents even though they contribute mitochondrial DNA to offspring. In this paper, I examine the way that the Human Fertilisation and Embryology Act in the UK manages the question of parentage. I argue that the Act breaks the link typically made between genetic causation and genetic parenthood by redefining genetic causation solely in terms of nuclear genetics. Along with this, mtDNA is construed as a kind of supplement to the nuclear family. Drawing on the account of the supplement developed by Jacques Derrida, I argue that mtDNA and the women who donate it are seen as both essential to establishing the nuclear family but also exterior to and insignificant for it.