Venus, the amazing split cat

September 2, 2012 • 6:38 am

I saw this cat on Facebook, where she has her own page.  Venus has apparently gone viral (see here, for instance) because of her “split face” appearance, which affects not only coat color and pattern, but eye color.

Now I could explain the genetics and developmental biology of the coat color, and why Venus would have to have been a female, but over at her website Planet of the Apes, Faye Flam has already done it, so go read her explanation. Note that Faye doesn’t explain the different eye colors, nor does National Geographic’s piece on Venus. Savvy readers may try their hand at this problem.

As for me, I don’t know why the eye colors are “split” along with the face. Eye color depends on genes different from those involved in coat color, so this may be a rare coincidence of somatic mutation (for eye color) that happens to accompany early inactivation of one X chromosome that carries coat color.

Venus’s Facebook page also has a diverse album of “split-face” cats and dogs.

h/t: Ant, Jon Losos, and many other readers who emailed me about Venus

27 thoughts on “Venus, the amazing split cat

  1. Flam’s analysis seems a little simplistic. Fur color is not a single-gene trait, as indeed implied by the mention of the black/agouti gene.
    But even black fur results from the expression of several genes, including those that code for enzymes involved in melanin synthesis, as well as genes that determine the expression (or ‘insertion’) of melanin into morphological structures like eyes and fur. (Examples include the genetics of black/chocolate/golden labrador retriever dogs and the color of their noses, also feather color in budgies.) Eye color (like feathers) also involves structual optical scattering effects–not pigment–that produces the blue-eyed phenotype in the absence of melanin.
    There is also no green eye pigment. AFAIK the green-eyed phenotype results from the addition of a small amount of melanin to the blue-eyed phenotype.
    The existence of black-furred blue-eyed cats (I googled) means that different genes affect the insertion/expression of melanin in eyes and fur.

    So my guess is that this is a green-eyed cat with melanin synthesis impaired on one side of the face. Blue eyes with melanin-free orange and white fur on one side (the orange pigment is phaeomelanin, from an alternative allele to the important (eu)melanin gene on the X chromosome); black fur and melanin-inclusive green eyes on the other.

    1. …but the existence of green-eyed orange-furred cats suggests I’m wrong. And/or that it’s more complicated.

      1. This post made me go and look at the eye color of all my cats.

        The black ones and the gray one all have green eyes. The white and orange one and the orange and gray tortoiseshell also both have green eyes.

        Go figure. L

  2. Regular tortoiseshell with some lucky/unusual neural crest migration. Our tortie has a “seam” down her belly that is marmalade stripes on one side and black on the other.

    Cat eye and coat colors are genetically related.

    1. Yes, some have speculated that Venus is a tetragametic chimera. This is very rare in most mammals, including cats. I think we should try to explain this by the normal genetics of coat and eye color in cats before thinking she’s a chimera.

      Chimerism is really interesting. There was a case where a woman needed a transplant of some kind and when doctors screened her children, they were surprised to find that the results showed that it was impossible for two of her children to be her children. Due to her chimerism some of her ova were from a different cell line than her blood cells, so there was a mismatch between tests done on the mother’s blood and tests on the children.

      1. “the results showed that it was impossible for two of her children to be her children.”

        Aristotle would have had something to say about that case of A=~A.
        The simplest fix is “it seemed impossible…”

        Only motherhood is certain….

  3. It is common in certain color-patterned Nigerian Dwarf goats to have one blue eye and one brown eye.

    It is also fairly common in Australian Shepherd dogs, and less common but not unheard-of in Border Collies. L

  4. If this is the same cat I’ve read about elsewhere, they call her a Chimera cat. The impression I got from the other article was that she was her own twin and the embryos fused, but I could be wrong. The article basically said she looks like two different cats because she technically is.

  5. If this is the same cat I’ve read about elsewhere, they call her a Chimera cat. The impression I got from the other article was that she was her own twin and the embryos fused, but I could be wrong. The article basically said she looks like two different cats because she technically is.

  6. Cats with eyes of different colors are, while not common, by no means the rarest of the rare. Google responds well to the query “cats with different eye colors”, while Wikipedia files this under “Odd-eyed cats”. To steal Wikipedia’s thunder, the phenomenon is connected with the genes governing coat color/pattern.

    No point in repeating more.

    Plenty of photos on Google images, by the way.

  7. The way I heard it, the iris develops from the same embryonic tissue as the skin. If the embryonic cell that then goes on to form the iris also carries expressed genes for the white spotting factor, then the iris is blue. Venus is a calico, so she is expressing some spotting factor genes. There is a nice discussion of coat color in R. Robinson, “Genetics for Cat Breeders.” Pergamon, 1971. I don’t know if it is still in print.

  8. Venus offers a nice example of the dynamics underlying “gene expression”, would that those presuming to know could stifle their dogma and plumb it.

  9. Remember the Star Trek episode where Frank Gorshin was half-black and half-white chasing another guy who was black and white on the opposite sides? Maybe that cat is from that planet.

    1. Yep, that STTOS episode was called “Let That Be Your Last Battlefield”. Lokai and Bele, the two black and white aliens were from the planet Cheron, in the Colesack Nebula.

  10. Shouldn’t she be deaf in one ear? I thought that blue-eyed cats were deaf (Darwin said that they generally are in The Origin)?

  11. Seems like a chimera to me.

    I have known many dogs with mismatched eye color.

    I have also know one human with one blue eye and one brown. It usually took people a while to figure out what looked so odd about him.

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