Demystifying the Munchkin Cat

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You may already have heard about the Munchkin cat, the ‘Dachshund’ of the cat world.

But what you might not know is that it might not actually be a breed but a (cute) condition.
“Gasp! Doesn’t Wikipedia say Munchkins are a breed of cats”, you’d say? Only very generally, much like you would consider short people a “breed” of people.
And Wikipedia gives the clue away:

“The Munchkin comes in all coat colors and patterns. It also comes in a long-haired variety which is shown in a separate Munchkin Longhair category. The short-haired variety has a medium-plush coat while the long-haired has a semi-long silky coat.[1] TICA rules for outcrossing allows the use of any domestic cat that does not already belong to a recognized breed. Similarity to other breeds is grounds for disqualification. Non-standard Munchkins are not allowed to be shown”

The fact that it comes in all coat colors and patterns and hair length — meaning, any breed will become a Munchkin if it inherits short legs — makes the Munchkin more of a leg length breed than a collection of true-breeding characteristics that make up a real breed.

Picture this: If you mate a Munchkin cat with an ordinary cat (even a stray tabby), half of the kittens will become Munchkin. That’s because the Munchkin gene is dominant. And, since practically all normal mammals have to have two copies of a particular gene — in this case, the gene influencing leg length (and there are a lot of genes, some have functions still unknown), the Munchkin gene overcome the normal gene for leg length.

So just one crossbreeding will get you Munchkin kittens in half of the litter? That’s shorter than the normal years it takes to develop a breed.

Here’s another clue. Virtually all Munchkin cats are, for lack of term to use, “half-breeds” — that is to say, there is no living pure-bred Munchkin. If you breed a Munchkin cat with a Munchkin cat, simple Mendelian inheritance would dictate that one-fourth of the litter will be normal-legged, half will be Munchkin, and one-fourth will be dead: the pure-bred Munchkins.

That is because pure-Munchkin kittens have two copies of the Munchkin mutation in the gene that influences leg length. And two copies of the Munchkin mutation proves deadly (“deleterious” in genetics)#.

If you give the symbol ‘M’ to the Munchkin mutated gene (capitalized because it’s dominant) and ‘m’ to the normal leg length gene, a healthy Munchkin cat would have this combination of leg length genes: ‘Mm.’

Normal legged cats would be ‘mm’. If you breed ‘mm’ cats with other ‘mm’ cats, you’ll never get Munchkins because they do not have the ‘M’ gene.

Purebred Munchkin cats (which die before or shortly after birth) would be MM. Since only the ones with the same genes in the gene pair can be considered purebred, hence a true breed, The Munchkin cats you’ll be able to get are not a true breed. And that is a good thing.

Munchkin Kitten Video