#mackerel TORBIE and a tuxedo and a MALE

[identifyingcatsinposts]

Chimera! Head and left side is black and right side of body is tortoiseshell black mackerel tabby; he has low white spotting (bi/tricolor pattern is tuxedo without gloves with a blaze). He is a Persian/Munchkin (Minuet).

I’ve seen a lot of people in the replies and reblogs not understanding his genetic makeup. I’ll do my best to answer some questions about Bruce and chimerism. Putting a cut in because it’s long, but keep reading to learn something new!

A chimera cat has multiple sets of genetic material in different spots on its body. If the material came from a fertilized ovum that underwent a somatic mutation, it’s mosaicism; if from two fertilized ova that fused into a single fetus, it’s chimerism. For the purposes of this explanation, I’m lumping both mosaics and true chimeras under “chimera”, like most non-geneticists do, but there is a difference.

Not all chimeras are easy or even possible to tell apart from non-chimeras, but those that are can be identified because only part of their body displays a gene that always displays over the entire body. Here’s an example: the easiest kind of chimera to spot is dilute/non-dilute. If a cat is part black and part blue with clear lines between the colors, that cat is without question a chimera. Chimeras can be reasonably identified if they express any mutually exclusive genes in patches: dilute & non-dilute, black base & different black base, tabby & self, pointed & non-pointed, shorthair & longhair, etc. though in order to be verified, genetic testing needs to be done. Most chimeras probably go unnoticed because the genetic differences between the ova simply weren’t significant enough to appear, or they appeared in a manner consistent with a different gene, making it seem that they were that gene instead. This is what happens to most red and black female chimeras. If a cat contains fused genetic material that is red & black or red/black/tortie & tortie and appears female, the cat will be perceived as a tortoiseshell, even if neither DNA set is O/o (tortoiseshell).

Bruce is clearly a true chimera, although he does need to be genetically tested to be certain. Him being tricolor and male could in a vacuum make him a XXY male calico with an extremely odd pattern, but the tortoiseshell side contains obvious patches of black tabby, which is impossible in conjunction with patches of solid black. Mosaicism tends to be a) far more localized than Bruce’s colors allow for and b) generally only causes a single change (while Bruce is, at the absolute bare minimum number of genetic changes, going from A/a -> a/a and O/o -> o/o) and so although it isn’t impossible to have two massive somatic mutations covering the exact same areas, he’s almost certainly a true chimera.

Here’s a couple corrections for misconceptions I saw in the rbs and on other websites:

A stray cat having red and black makes for a great reason to call her a good girl instead of a good boy if you don’t have the wherewithal to check the equipment (since the vast majority of torties are female), but not only can chimeras be any sex, non-chimera male torties exist too! The most common type are XXY males, who are intersex and infertile but perfectly healthy.

Not only CAN chimeras not have the face split — and not only DO most chimeras not have the face split — but most cats with a face split (where one half is one color and the other another) are not chimeras at all! If the split is in the colors and patterns typical to a tortie or torbie, it’s an uncommon but perfectly regular tortoiseshell or calico pattern. Also, if the face is half white, especially if the rest of the cat has a decently high amount of white, that’s probably not a chimera either. Having heterochromia doesn’t make a cat a chimera either, even with the face split.

Chimerism isn’t inherently an intersex trait — it only causes a cat to be genetically of two sexes if a true chimera’s fused ova are different sexes or (on occasion) if a mosaic’s somatic mutation occurs in the genital region. Whether that counts as intersex depends on your definition: most chimeras will have genitals that work exactly like non-chimeras, and cats don’t really have obvious secondary sexual characteristics to be affected by their chimerism. Bruce here is presumably a regular tomcat where it counts based on the original post, but some of his skin and fur is female.

Unlike most tortoiseshell male cats, Bruce is probably not infertile. Most tortoiseshell males have Kleinfelter’s syndrome, an intersex condition which does sterilize them. Chimeras are usually perfectly capable of breeding (with rare exceptions and the exceptions all cats are subject to). Despite that fact, Bruce would breed as though he was a normal black cat: even though he has orange and tabby patches, he will not be able to pass the orange or tabby gene onto kittens because his reproductive organs will only carry gametes derived from the ovum that lent him his black side.

(He probably should not be bred, but not because of his chimerism. This isn’t the point of the post, but I feel obligated to note that the Persian breed standard prioritizes several harmful conditions and Munchkin dwarfism is by nature homozygous lethal and heterozygous extremely harmful, making Minuets exceptionally cruel to intentionally breed.)

Other well-known chimera cats include Dawntreader Texas Calboy, Pretty Boy Floid, and Skye Blue Humphrey Bogart. “Venus the Chimera Cat” is the modern-day best-known cat under the name “chimera”, but she could easily be an unusually patterned tortoiseshell (she hasn’t been genetically tested and her pattern is plausible enough to disqualify her from the “possible chimera” status that a cat can achieve if all other possibilities have been ruled out) and she isn’t a good face for chimera cats as a whole because of the misconceptions split-faced tortoiseshells have spread about what chimeras look like. Another popular possible chimera is Quimera, who is also an unconfirmed split-face calico, but she’s more likely to be a possible chimera, not because of her face or eyes, but because of patches of what resembles black tabby on her body despite her solid black facial pattern.

Disclaimer on this post especially: I am not a geneticist. I am a hobbyist that happens to know a lot about cats. If you know any scientific information that contradicts me, please do send me your sources and I will correct myself.

[sparrowminder]

can you list some possible parent cat color combinations that could breed a classic marked torbie cat? i have a warrior OC that’s a torbie with classic tabby markings and i’m trying to have it at least somewhat genetically accurate in terms of parents. I just don’t want the parents to be like...a grey tabby and a black cat.

Sure! 

Here’s the requirements:

Your combinations for sex-linked red are as follows: red female + not-red male, not-red female + red male, or tortie female + any male.

At least one parent must be a non-dilute color (black, cinnamon, chocolate, or red). 

At least one parent must be tabby. What kind of tabby doesn’t matter - any combination of tabbies can produce classic kittens.

Neither parent can have over 50% white spotting. (Actually, they could, it would just be pretty unlikely. But only one of them could have over 50%). This doesn’t include epistatic white, that’s fair game for either or both of them.

So for a few quick suggestions, because it’s fun:

A mackerel torbie molly and a cream ticked tabby tom with tuxedo white.

A pure white molly and a grey classic tabby tom.

A fawn spotted tabby molly and a red classic tabby tom.