[c!tommy]

Ll/BB/oo or oY/DD/aa/wsw

Thank you so much for your help, Bees! I'm absolutely terrible at genes lol.

[I Like Bees]

Hello! Disclaimer before I give you any information - I'm not Simonpet (the resident geneticist for Soft) nor do I work for Soft; I'm just obsessed with correct torties. 😅

There are two "types" of color in cats: eumelanin and phaeomelanin. For the sake of using readable words, I'll call them black (eumelanin) and red (phaeomelanin) from here on out.

Tortoiseshells exist due to red being linked to the X-chromosome and because of some complicated stuff I won't confuse you with. Basically, though: they're female unless there's a mutation or something else weird going on.

Normal tortoiseshells follow what I call "The Tortie Rule":
Tortoiseshells always combine a black and a red color, and always of the same form.
"What does that mean?" you ask. It's actually not as complicated as it sounds!
I'll list all the colors, then explain how, by this rule, they can be mixed into torties.

The possible 'black' colors are black, chocolate, and cinnamon.
Black dilutes to blue (gray). Chocolate dilutes to lilac. Cinnamon dilutes to fawn.

The possible 'red' colors are red. Just red (also called ginger or orange).
Red dilutes to cream.

The first part of the Tortie Rule ("always combine a black and a red color") means exactly that: when making a tortie, one of the two colors needs to be from the list of black colors, and the other one needs to be from the list of red colors. You can't have a black-chocolate tortie because both are black colors. You can't have red-cream tortie because both are red colors.

The second part of the Tortie Rule ("and always of the same form") means that non-dilute colors must be combined with a non-dilute color, and dilute colors must be combined with another dilute color. You can't have a black-cream tortie because black is non-dilute and cream is dilute. You can't have a lilac-red tortie because lilac is dilute and red is non-dilute.

If a color combo passes both halves of the Tortie Rule, it's a possible tortoiseshell combo!
Essentially, the possible tortoiseshell color combos are as follows:
Black-red. Chocolate-red. Cinnamon-red.
Blue-cream. Lilac-cream. Fawn-cream.

Black and white cannot be combined into a tortoiseshell.

However, white spotting can be added on top of a tortoiseshell, making it a tortie with white or a calico, depending on how much white there is. Here is a tortie with white example, and here is a calico example. Note that the white is added as an additional third color, not as a replacement for one of the two base tortie colors.

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How this Pattern Actually is Possible:
(aka, the exact opposite of what I've been saying)

There is actually a mutation (known as a 'brindled bicolor') in which the red colored fur is replaced with white.
Genetically, the cat is a normal tortoiseshell, but, appearance-wise, it could look similar to the cat you drew.
This mutation is very unusual, though, and you won't see it very often.
In Soft, I believe this would be limited to milestones?

Another mutation that can cause something similar to this cat is vitiligo. It's also very rare. Patches of white appear on the coat and then gradually cover the cat until they're entirely or mostly white. Here is an example!
In Soft, this is also probably limited to milestones.

(Don't quote me on the milestone thing, though. I couldn't find anything about that on the main page; it's just an educated guess.)

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If you go with this cat has no odd mutations, the cat you've drawn would be considered a solid black with white spotting.
(Note, however, that cats usually don't have white spotting this irregular without it being a mutation.)
The genotype, therefore, would be as follows (using Simonpet's system of explanation):

• Ll: This cat is short-furred carrying long fur. (They don't need to be a carrier; I'm just sticking with what you wrote.)
• BB: This cat's base color is black.
• oo or oY: This cat has no red and isn't a tortoiseshell. ('oo' is if the cat is female; 'oY' is if the cat is male.)
• DD: This cat is not dilute. (If they were, they would be gray rather than black.)
• aa: This cat is solid (has no tabby patterning).
• wsw: This cat has a little less than half (50%) white spotting.

If you'd like help with any of your other entries (and it's alright with Simonpet and other Soft staff?) or just have general cat genetics questions you'd like answered, you're welcome to message me questions! <3

[Simonpet]

First, I’d like to thank @Bees a ton for this in-depth explanation into how torties work. We currently have no plans to include the brindled bicolor mutation but we do have a Karpati mutation (similar to vitiligo except without the negative effects) that shows up in Fall cats and their hybrids! However, your second explanation of this cat being a solid black-and-white cat is correct judging by what I see in the design and genetic string. I also came up with the same edited string (aa / BB / DD / Ll / oo or oY / wsw) which would showcase the fact that this cat is solid, black, not-dilute, shorthair carrying longhair, not-ginger or tortoiseshell, and has white spotting and is what I see you, @mr. krabs, edited it to!

Second, to answer your question/comment, @Bees, I am totally fine with people stepping in when they have some background in genetics! The more the merrier is what I say. <3