Instead, defective mitochondria are being replaced with mitochondria from a healthy donor. This technique is only valid for diseases involving defective mitochondria.
The mitochondrial DNA is responsible for very very little of the genetic material that defines who a person is, essentially limited to how effective the mitochondria are at their job. This is around 0.1% of the total genetic code.
Mitochondria are organelles in our cells that break down molecules to provide energy for the cell, in the form of ATP. They have their own genetic code completely distinct from the host cell's DNA.
The mitochondria are replaced in either the egg OR in the embryo. In both cases this is done by removing the nucleus (containing the cell's genetic material) from the cell that has defective mitochondria and transferring it to a donor cell with healthy mitochondria. The donor cell's nucleus is completely removed.
The mitochondrial DNA is passed down from the mother alone, whilst the DNA in the embryo is formed from both the mother and father. For this reason mitochondrial DNA has much less genetic diversity. Mitochondria 'reproduce' by binary fission which is similar to bacterial cell division and produces little variation in its genetic code, whilst egg and sperm go through meiosis allowing the genetic code to be mixed.
Opposition seems to be coming from two camps.
- Those who don't like the destruction of the donor embryo (when that method is used),
- Those who think this is the start of ever more invasive genetic modification of humans, or so called "designer babies"