There are parts of the Dna responsible for leading to the formation of what are called mitochondrial cells, which are essentially the energy storage devices within cells. This particular part of the DNA has nothing to do with eye colour, height, hair colour, race, skin tone, and all the characteristics we commonly associated with being hereditary traits in children. The only difference alteration to this DNA makes is to stop the inheritance of mitochondrial disease in the child, and this particular part of the DNA will be the only part legally allowed to be altered, and only in the way mentioned.
What it basically means is that a couple with mitochondrial disease can have offspring that are entirely their own in every meaningful way (by blood, eye colour, hair colour, skin tone, facial features, bone structure, everything) without having mitochondrial disease.
Not saying I agree with it, but that's basically what it is. It certainly is not "creating abominations" or "creatures from Greek mythology".