UK MPs have voted overwhelmingly in favour of not needlessly inflicting horrible metabolic diseases onto innocent children by approving so called 'three parent babies'. Link
However it is very misleading to call them three-parent babies since only two parents contribute over 99% of the DNA in the child, and the so-called third parent only contributes a tiny fraction of DNA present in the mitochondria (only 37 genes compared to 20,000 in the nuclear DNA). Indeed, the 'third parent' is contributing less to the child than
Neanderthals (assuming the child isn't African) which interbreed with
humans 40,000-70,000 years ago, and how many of us want to claim a
Neanderthal as a parent?
Furthermore mitochondria aren't even very human, they were at one time free-living bacteria who formed a symbiotic relationship with an ancient single-celled organism. This partnership was so successful it went on to evolve into all eukaryotic organisms (everything multi-cellular plus things like amoebas). The symbiont evolved into what is essentially just the power plant of the cell with almost all of its original genome and cellular processes shifted to the host cell (so even the mitochondria of these three-parent children have many many parts derived from the two parents contributing nuclear DNA). So just how 'human' is the DNA contributed by the 'third parent'?
To make matters worse the human nuclear DNA is chocked full of selfish DNA which likely used to be some sort of virus and many of these originated even more recently than mitochondria (the most common in the human genome is only found in primates), indeed many current viruses will integrate themselves into the human genome and in theory could be passed on to children. Together these two sources account for roughly the same amount of DNA in a human cell as the mitochondria. Thus do humans as have bacteria and viruses as parents? Are we one organism or an amalgam of many?
What is obvious though is that taking the mitochondria of one person to replace the defective ones of another person isn't nearly as weird as what nature has done to produce ourselves, so it cannot be dismissed as creepy or inherently wrong.
