My last post prompted a reader to send me photos of her tortoiseshell cats. [Thank you!] Such a flow of cat pics is of course unconventional in cat blogging, but it gives me an opportunity to point out that it’s only some of the much rarer male tortoiseshells that are the true chimeras, mixtures from two distinct embryos of different colours; and that even those obviously aren’t interspecies chimeras, just as the human example I linked to isn’t.

Since female tortoiseshell cats are a gross manifestation of the phenomenon of sex-specific gene expression knowns as “X-inactivation“, and so-called “Barr bodies” in individual cells are a microscopic one, this also gives me a chance to link, radio DJ-style, to an example of the kind of Frankensteinian activity even relative beginners in the lab have been up to for years.

One of the first things I learned to do as a research assistant was to take blood from human volunteers, purify out the white blood cells, and transform them with Epstein-Barr virus into immortal cancerous tumours. Then I grew them in incubators. It’s the sort of thing no one in the business gets the slightest bit upset about, but it sounds deeply yucky to many outsiders, especially when they are told that you have to be careful to keep the growing cell cultures away from their donors for fear that you might give them a lymphoma that their immune systems would be unable to fight—a real consideration when the people you have taken blood from are, for convenience, often your co-workers.