Olivia Judson, a.k.a. Dr Tatiana, made an informative post on cybrids earlier this week. It concerns the technique --- it is fair to describe it as controversial, when human DNA is involved --- of transplanting a small cell of one species into the egg of another, in place of the target cell's own nucleus. The nuclear DNA then ends up being entirely from the transplanted species ...
... but the nucleus is not the only thing with DNA. Some organelles, specifically the mitochondria, have it too, and mitochondria are important. Whether the (say) human/bovine mitochondrial differences, or other differences between human and bovine eggs, are important, I'm not well-placed to judge.
I was struck by the statement that "A mammalian egg may contain as many as 200,000 mitochondria": I had no idea that it could be so many. (Lots of cells have only a handful.) This seems to be another of those areas where even people like me, members of the scientific community in good standing but with only rudimentary biology, know some of the facts but not their relative importance or proportion: where we miss the "feel" of the thing. As I have learned over the years, the interior of a cell can be a very complicated, crowded, non-soup-like place. This is not what I was told at school.
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