A fertility treatment which eliminates hereditary disease by engineering babies to carry healthy DNA from a third biological parent could be legalised next year

I thought the whole point of the Daily Mail was to keep the crazies to one part of the internet - they seem to be spilling over.

Yes and we will see worse to come I suspect. Stupidity is terrifying and unfortunately way too common these days.

No. Each cell has something called a mitochondria. It's basically a cell inside a cell. It produces ATP which is the energy molecule needed for the cells activity. Enzymes and other stuff are needed to produce ATP quite rapidly, so mitochondria has evolved to include some DNA. This allows it to rapidly syntheses the proteins needed to produce ATP. Sometimes the DNA in the mitochondria is damaged or "bad". This means the wrong proteins are coded for > less atp produced. Meaning less functions can be carried out by the cell etc etc. Overall it's pretty fucked up. This treatment allows healthy DNA to be implanted into the mitochondria, therefore allowing ATP to be produced normally. Then the offspring can live a perfectly healthy life like you and me. From the Daily Mail's POV he/she will have "3 parents". But practically with the exclusion of the mitochondria DNA he'll just have 2.

but I have a question.

Then try reading the article....