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Merry Christmas dear pet hoomans! We hope you are all having a wonderful time with your families today. To help brighten this blissful day even more, we would like to tell you one of the most meowgical stories of feline genetics – the story of the Chimeras! In Greek mythology, a chimera is a monstrous fire-breathing, three-headed hybrid creature. In cat terms, luckily, a chimera is not scary at all! Chimeras, as we here know them at Basepaws are gorgeous and breathtaking genetic anomalies.

In Greek mythology, a chimera is a monstrous fire-breathing, three-headed hybrid creature. It was usually portrayed as a lion with a goat rising from its back with a snake for its tail. Homer described the Chimera in the Iliad as “a thing of immortal make, not human, lion-fronted and snake behind, a goat in the middle, and snorting out the breath of the terrible flame of bright fire.”

In cat terms, luckily, a chimera is not scary at all! Chimeras, as we here know them at Basepaws are gorgeous and breathtaking genetic anomalies. They are composed of parent cells with different genotypes which most commonly occurs by the merger of multiple
fertilized eggs. Due to the presence of two distinct genotypes, both expressing themselves in the phenotype, chimera cats are characterized with a mixture of tissues derived from different genomes. Isn’t that wild?!

What is a chimera?

In animals, chimeras are formed from at least four parent cells. They can either occur after two fertilized eggs or two early embryos fuse together into one organism. Thus, an animal chimera will carry two or more genetically distinct populations of cells,
originating from different zygotes. Each population of cells keeps their own genotype and their own characters. This results in the formation of mixture of tissues. During the organism development, there is a chance that the entire organs will possess
different genotypes. For example, the animal can end up with one organ solely composed of one population of cells, and another organ completely built from the other population of cells.

In an article on the The New Republic, Columbia University Professor of Genetics and Development, Virginia Papaioannou explained: “a chimera…is made up of cells from at least two different original embryos. If they fuse together early enough, they will become a single organism whose genetic input is from two completely different individuals.”

In case two or more genetically distinct cell populations emerge in the same zygote, then this condition is called a mosaic and not a chimera. This is because all the cells originate from the same original organism that genetically diverged
due to genetic mutations. They don’t come from two different individuals.

Chimeras can be created artificially too

Chimeras are often artificially produced in biological research. This is conducted by selective transplantation of embryonic cells from one organism onto the embryo of another. However, this should not be mixed up with hybrids and hybridomas!

Hybrids are formed by the fusion of two gametes deriving from two different species into one single zygote. Hybridomas are created by the merger of two cells of different species into one cell. What is the core
difference exactly, then? Well, while hybrids and hybridomas have cells deriving from both parent species, chimeras will have cells deriving from only either of the parent species.

How common are chimera cats?

While chimerism among animals is exceedingly rare, among cats, chimeras are really not all that rare. In fact, Leslie Lyons, a professor at the University of California, Davis, explains that most male tortoiseshell cats are
most probably chimeras. The tortoiseshell coat in male cats indicates the presence of an extra X chromosome – which is why this coat color is so rare among the boys in the first place.

Female tortoiseshell cats have two X chromosomes to begin with, so they don’t necessarily have to be a chimera to sport this coat coloration. Males, however, who normally carry one copy of the X chromosome, have to have an extra copy in order to be tortoiseshell,
and therefore are much more likely to be chimeric.

Chimeric feline celebrities

Meet Venus, the greatest cat celebrity out there! She is lovely! And how did she earn this title? Because she takes the chimera mystery to a whole new level! Her perfectly split face and
two differently colored eyes divided the internet in two teams. Does she really carry different DNA on each side of her face, or are we looking at a typical example of mosaic? Her coat and eyes can be easily explained with both scenarios.

Venus

Yes, it is possible that this beautiful cat carries two (or more) cell populations, both expressing themselves in her phenotype. However, since she is a female who naturally has two X chromosomes, her coat may be a typical tortoiseshell coat. It is possible
that “the black coloration was randomly activated in all the cells on one side of her face, while the orange coloration was activated on the other, and the two patches met at the midline of her body as she developed.” – explained Lyons.

But Venus also has a blue eye. Her heterochromia can be explained with a white-spotting gene, but she only has one white patch on her chest. Is that enough to explain the blue eye? We don’t
know. “She is a bit of a mystery.” – concluded Lyons. Only a DNA test could resolve this little feline puzzle.

Other felines who took the internet over with their possible chimerism, completely oblivious to their fame, are Quimera and Narnia.

Quimera  (also featured in the headline photo)

Quimera is a two-faced little kitty coming from Argentina. Just like Venus, she may be either chimeric or mosaic. Whatever the case, Quimera is taking the internet by storm. She is described by BoredPanda as “…just gorgeous! Her blue eye especially appears like some kind of precious stone, bright and beautiful and an utter contrast to her other eye. The colour split continues down her chest to her front legs, with the sides reversed.”.

Narnia De La Grace

Narnia De La Grace, a French diva, is a one-year-old with light grey and black fur on his head, separated evenly in a remarkably straight line. His human companion, Stephanie, describes him as “a little bit shy when he is in a new place, but a very soft and friendly cat. He doesn’t know he is so special, but I have a very strong link with him, he is my little baby.” According to DailyNews, Narnia has become a hit in France with requests for him to appear on television and at cat shows.

Although less commonly, chimerism occurs among other pets too. This is Tiger, an intriguing pup whose DNA results confirmed she was a chimera Labrador! “Tiger has personality plus. She is a very happy girl. She doesn’t take herself too seriously. She is more than a bit of a diva and a rascal. – described Tiger’s pup parent.

Tiger

Chimeras are bizarre but striking genetic anomalies. While rare among animals, in cats they might be more common than we think. Do you think your cat is its own non-identical twin? Share with us, we love hearing your stories!