[burning_hamster]

I disagree.

> I think it would be better to describe this as an ‘organelle’ transplant as it would be easier for people to understand and discuss.

Unlike previous attempts, the donor mitochondria are not transferred into the mother egg. Instead the donor cell is denucleated, and the nucleus from a mother's egg is transferred into the denucleated donor cell. Consequently, there is a wide variety of donor specific material, which may influence the early stages of development and only "wash out" after a number of cell divisions.

> But calling it a 3 person baby is unhelpful and misleading as IMO mitochondria DNA is of a different category to chromosomal DNA.

How so? Arguably, mitochondrial genes are much more essential than most nuclear genes.

1. Mutations in any mitochondrial gene often have dire consequences, whereas variants in nuclear genes are much more frequent.

2. Mitochondrial DNA is the most expressed in pretty much any cell by a huge margin. Mitochondria express 13 (IIRC) protein coding genes and two dozen other RNAs. Those 30 odd genes often make up 1-5 % of a cell's whole transcriptome. Only genes coding for ribosomal RNA are more strongly expressed.