I am referring to "3 parents baby" discussed e.g. here http://www.economist.com/news/leade...ial-diseases-should-be-permitted-law-powering . AFAIU they take the egg of mitochondria donor, remove its nucleus / DNA and transplant into it the mother's DNA, thus creating an egg with good mitochondria and, allegedly, correct / undamaged DNA. So I am wondering, why don't they remove (destroy?) mitochondria and transplant new ones into mother's egg instead, not touching the DNA at all? Are there too many mitochondria in the egg to easily achieve that? Or what is the underlying rationale?