On CSI last night the peg on which the segment hangs was a chimera -- a human with two distinct DNA types. I had not heard of this word used in that sense before so I googled it.

In the very rare situation mentioned above, a fraternal (or sororal?) twin's body is absorbed by the other twin while still in the mother's uterus, and the resulting individual can have two types of DNA. One twin's DNA might be in one organ, and in another organ, the other twin's DNA would be found. (Of course if they were identical twins the DNA would be the same.) To the analyst, it would appear that the chimera's DNA came from two different but closely related people.

But it seems there are other kinds of chimeras: animals of different species, animal-plant, animal-bacteria, and so on. (None of these latter types would come up in a criminal investigation, although the first type, the human-human chimera, might.) And as far as I can tell these do not often occur in nature, but are created only in the laboratory, as the result of gene-splicing.

But nature has done some gene splicing, and our human genes have some bacteria or virus trash in them. At some point in our past, a virus insinuated its DNA into some human ancestor's DNA and it hung around: by the very nature of DNA, it replicates itself; it survives.

Question: When does science get too weird, so that we would feel compelled to stop a particular kind of research on ethical grounds?

I think that would depend on the purpose of the exploration and if anyone is being harmed. In most cases though I'd say the more we know the better. What if the chimera needed an organ? They'd need to know the DNA to match, wouldn't they?

When will science get too weird?
Mabye never.
Science is making new thing possible and the splitting of Genes could be a very important one.
If, God forbid, we have children born with some kind of defect, we would welcome science to help us, if we have a loved one with some disease, we would welcome science. The world is opening up with new inventions that are helping everyday life, and now if we could just find one to cure poverty.

Oh, we already have the knowledge to cure poverty. We just lack the will to do it. Science can't help us with that one.