In CryptoKitties, genes are either primary or hidden based on their location in the Kitty’s genome sequence. A primary gene’s dominance or a hidden gene’s recessiveness determines its likelihood of getting passed on to a cat’s offspring. Primary has a higher chance of getting passed on, hidden a lower chance. You probably figured that out on your own.

A Kitty’s genome is made up of a string of blocks, each containing four genes. Every block of four represents one trait: eyes, fur pattern, body colour, et cetera. Each block has one primary gene and three hidden genes. The primary gene is the one that gets manifested in the cat’s appearance. The hidden traits aren’t visible in your cat’s appearance but may get inherited by the cat’s children. The primary trait has a 75% chance of getting passed on, with a 25% chance that one of the hidden traits will pass on instead.

Above is a visual breakdown of a Kitty’s genetic code. Cute, right? We know. The primary trait, represented by P, is the visible trait that determines the cat’s appearance. The remaining three genes (H1, H2, H3) are the cat’s hidden traits, the ones that don’t affect its appearance but may get passed on to offspring.

Within each block of four genes the probabilities of traits getting passed down looks something like this. The farther down the sequence a hidden gene lives, the less likely it will be inherited.

So imagine we were to breed these two Kitties together (such romance). Let’s look at their genes to figure out what body pattern their kid might have.

The possible patterns are calicool, luckystripe, totesbasic, and spock. Their probabilities break down like this:

Calicool: 37.5% + 37.5% + 0.8% = 75.8%
Luckystripe: 9.4% + 9.4% = 18.8%
Totesbasic: 2.3% + 0.8% = 3.1%
Spock: 2.3%

Since it’s a primary gene in both parents and also appears as an additional hidden gene in one Kitty, calicool is by far the most likely. Second is luckystripe, which is also present in both parents as a hidden gene. Finally there are totesbasic and spock, both hidden genes with slim odds of passing on.

By breaking down a Kitty’s genetic code like this it’s possible to sketch an idea of what its offspring might look like. This is important if you’re looking to breed for specific traits.

Of course, if you don’t feel like crunching the numbers yourself, tools like Kitty Calc will do it for you. Plug in the ID numbers of two cats you want to breed, and Kitty Calc’s gene reader will read your kitty’s genes and lay it out in an intuitive and positively fetching interface (we used Kitty Calc to make figure 1 above).

An aside: When CryptoKitties started getting popular, a lot of people made “breeding calculators” even though the cats’ genetics weren’t yet fully understood. These calculators relied on anything from wild guesses to machine learning, but basically all of them were inaccurate to some degree.

Now that the genetics are better understood and the smart contract analyzed, it’s possible to create breeding calculators that are far more accurate. Unfortunately, many of the less precise ones are still floating around online.

There are, however, a few really good calculators. We recommend KittyCalc.co. KittyCalc not only shows the breeding outcomes but also specifies which traits may appear as a result of mutation or inheritance.

Mutations

Of course, that’s not the end of the story, genetically-speaking. Sometimes genes will mutate. No, your Kitty will not have superpowers. But it might get a rather unexpected trait.

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