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 ye

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 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.