My ears were burning, and I wondered why... then checked my email, and found:

If you had access to two cells --- one from a woman and one from her daughter --- would you be able to tell which was the mother and which was the daughter?

For a human, or any other diploid organism, the answer is yes, easily. (By "easily," I mean that there are all sorts of cool and unexpected things in genetics that make it trickier than what I learned in 9th grade biology, but even the simple model provides an answer to your question.) "Diploid" means you have two copies of what we glibly refer to as "the human genome", though of course your two copies, and those of every other human, are all slightly different (differing at roughly one letter per 1200). Your two copies came, one each, from your two parents. But the copy you inherited from your mother isn't simply a reproduction of one of her two copies. (If that were the case, then fraternal twins would actually be identical 1/4 of the time!) Instead, during the creation of an egg, the mother's two copies of the genome line up with each other and somewhat randomly swap corresponding bits. So of your two copies of the genome, one came entirely from your mother, but that one is a patchwork mosaic of the genomes of your two maternal grandparents. So figuring out who's mother and who's daughter is as easy as labelling their genomes a,b and c,d and noticing which of them has the property that, eg, ccccccccccccc is the same as aaaabbbaabbbb. --Michael Kleber -- It is very dark and after 2000. If you continue you are likely to be eaten by a bleen.