This is basically what it sounds like. The chromosomes come from two people (still referred to as a “mother” and “father” at this point in history) and the mitochondria come from a third (female) person. The egg is implanted in the (first) female who brings the baby to term and gives birth, but I suppose there is no reason this has to be the case. The purpose (at this point in history) is to avoid certain rare genetic diseases, and this has worked effectively and produced healthy babies.

Mitochondrial donation treatment, or MDT, aims to prevent children from inheriting mutated mitochondria. The procedure involves fertilising the mother’s egg with the father’s sperm and then transferring the genetic material from the nucleus into a fertilised healthy donor egg that has had its own nucleus removed. This creates a fertilised egg with a full set of chromosomes from the parents, but healthy mitochondria from the donor. The egg is then implanted into the womb to establish a pregnancy.

I have no moral objection to this. Reproduction was always inevitably going to get higher tech over time. The problem is more that wealthy people will have access and others won’t, unless or except in places where governments make other choices.