[MrDrDr]

I think it would be better to describe this as an ‘organelle’ transplant as it would be easier for people to understand and discuss. Yes there is a donor (egg) and yes the new child will pass on the mitochondria to her children. But calling it a 3 person baby is unhelpful and misleading as IMO mitochondria DNA is of a different category to chromosomal DNA.

[gus_massa]

It's inheritable so it's more than a liver transplant.

I agree that DNA in mitochondria is much smaller than DNA in the nucleus. But in each person there are many mitochondria and they nay have slightly different DNA. And the DNA in mitochondria has a different variation than the DNA in the nucleus. So it's difficult to weight both.

Can we say 2.1 parents? A long time ago I read that most binary classifications are not completely binaries, it's just that 2 options cover almost all the cases. (Are virus alive?) I guess integer classifications also have hidden corner cases.

I also remember from a biology book that in a lab they mixed two blastula(?) of small lizards(?) or something like that. They had different skin color and the baby had patches of both colors. Does that count as 2 or 4 parents?

[tialaramex]

Certainly Mother Nature is not obliged to have simple easy to understand binaries where it would be convenient for us and so if we think we see such a binary we should keep in mind that maybe we hallucinated it into existence because it was convenient and that's all.

[opello]

I agree wholeheartedly. This strikes me as the way science works. Theories are useful because of their predictive value. If we think of biological sciences as different than physical or mathematical, it seems we have set ourselves up for failure. Yet that seems like exactly the kind of perspective missing and trying to be pointed out by the earlier comment's attempted splitting of the difference to "2.1 parents" to me.

[SJC_Hacker]

It’s a binary that works in 99% of cases. Doesnt seem like a hallucination to me

[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.

[sidewndr46]

While it is a different category that chromosomal DNA, it is still an essential part of mammalian life. None of use would exist in our current forms without mitochondria

[pfdietz]

As I understand it, a human egg has about an equal quantity of nuclear and mitochondrial DNA. The mitochondrial DNA is highly replicated, though (about 100,000 mitochondria, each with ~16600 base pairs of DNA).

[burning_hamster]

I was going to call BS on this one, but after crunching some numbers, if anything this is likely an underestimate.

human nuclear genome size (haploid): 3.1 billion bp

mitochondrial genome size: 16 000 bp

1 human nuclear genome per egg -> 3.1 billion bp nuclear DNA

100 000 mitochondria, each with 1-10 genomes per mitochondrion [1] -> 1.6-16 billion bp mitochondrial DNA

So the ratio of mitochondrial to nuclear DNA in human eggs is on the order of 0.5 to 5.

[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC4988970/

[pfdietz]

Thank you for the tidbit that mitochondria each may have multiple copies of that genome.

[jungturk]

DNA can migrate between the nucleus and the mitochondria (and vice versa) so its not entirely black & white.

[gus_massa]

I've read about migration from mitochondria to nucleus, but I don't remember in the other direction.

Anyway, it's a very slow procces, IIRC like millions of years. We can ignore it in the human escale.

Also, both DNA use a sligtly different genetic code. From https://en.wikipedia.org/wiki/Human_mitochondrial_genetics

> For most organisms the "stop codons" are "UAA", "UAG", and "UGA". In vertebrate mitochondria "AGA" and "AGG" are also stop codons, but not "UGA", which codes for tryptophan instead. "AUA" codes for isoleucine in most organisms but for methionine in vertebrate mitochondrial mRNA.

So it's not as easy as cut&paste.