I first wrote about scientists producing human embryos with the DNA of three people in 2008. The new issue of Nature has an article on the researchers' progress.

The British team carrying out the study used fertilized eggs donated by couples undergoing fertility treatment, and which were unsuitable for in vitro fertilization (IVF). At this early stage the sperm and egg nuclei, which contain most of the parental genes, have not yet fused. The researchers removed these nuclei and transferred them into another fertilized egg cell which had had its own nuclei removed.

As very little cytoplasm was transferred with the nuclei, the transfer left behind almost all the mitochondria from the donor egg.

Neurologist Doug Turnbull doesn't think a contributor of mitochondria should be considered a parent.

Turnbull compared mitochondria to the power source for a laptop. “All the characteristics of the computer are stored on the computer. We’re just changing the battery,” he said. [Link]

For genealogists, it's a bit more complicated than that. Mitochondrial DNA has become a convenient way to trace maternal ancestry, and that only works if the DNA was contributed in the natural way. Someday we might have to distinguish between OEM batteries and those provided by third-party manufacturers.