Wednesday, September 5, 2012


I have blogged about cats many times: controversial cats, handsome cats, even 2-faced cats. But Venus (image above, video here) is the 1st cat in the Cabinet to demonstrate the tricky concept of chimerism. A chimera is a human or animal (here is a horse and here is a mouse) formed from 2 fertilized eggs or early embryos fused together. Each population of genetically distinct cells keeps its own character and the resulting organism is a mixture of tissues. (For a more detailed, but still understandable, definition, ask a geneticist.) Most male tortoiseshells are chimeras, with their mottled orange and black coat caused by an extra X chromosome. But female cats, which already have 2 X chromosomes, can sport that coat without the extra X. That means that Venus is not necessarily a chimera, explains University of California-Davis geneticist Leslie Lyons. "She is extremely, extremely rare," because her patches met at the midline of her body as she developed, and "She is a bit of a mystery," because her blue eye is typical of Siamese cats or cats with a lot of white fur. DNA fingerprinting of skin samples from each side of Venus would resolve her genetics, but wouldn't you rather just marvel at her?

Coincidentally, shortly after I learned of Jewel my friend Jody sent me the link to the scholarly article "Which Half Is Mommy? Tetragametic Chimerism and Trans-Subjectivity," about Lydia Fairchild and Jamie Townsend, women who have had to prove through chimerism that their children were their biological offspring even though DNA testing seemed to disprove it.
DNA-related posts:

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