The dog breed whippet can have a mutation in the genes that code for production of myostatin, resulting in the dogs having a huge muscle mass compared to other dogs from the same breed!

A few months ago I was trying to figure out which dog breed would be best for my family, and those of you who have followed my blog probably knows that we ended up with a whippet – a type of sighthound that looks a lot like a greyhound. However, during the research phase I came across a very interesting thing about the whippets, so today we will be looking at how genetics can make the whippets look like they have been eating steroids like it was dog treats!

The whippets are generally very slim, but just look at this “bully whippet”, and you can immediately see that there’s something different with him. Image by by Dana S. Mosher, Pascale Quignon, Carlos D. Bustamante, Nathan B. Sutter, Cathryn S. Mellersh, Heidi G. Parker, and Elaine A. Ostrander, published with the Creative Commons Attribution 2.5 Generic license.

As you can see from the image above, the muscle mass of this animal is obviously way higher than what you would expect, and it all has to do with a mutation in genes that control the muscle growth.

The genetics behind the bully whippet mutation

The protein in question is called myostatin, and is a member of the moykines – the proteins responsible for changes in the metabolism when an individual is exercising. Myostatin is pretty much responsible for inhibiting muscle growth so that we don’t keep growing our muscles forever after exercising. The protein is produced by the myostatin gene (MSTN), and if anything were to happen to this gene, the muscle production would be changed.

Animals have responded differently to mutations or deliberate changes in the MSTN genes, but most tend to get extremely muscular. This is exactly what happens with the whippet, and individuals who have mutations in both sets of the genes (remember that they get one set from each parent) will look like they are on steroids, and are called bully whippets.

The bully whippets will not only have more muscles, they also got a bigger tail, a broader head, shorter legs, and a pronounced overbite. They don’t really look like regular whippets at all to me, and if you compare the image at the top of the post to the one below this text, then I’m sure you can agree.

What a regular whippet looks like. Image by Ellen Levy Finch, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license.

How the whippets ended up with the “bully whippet” mutation

I don’t think most people think that the bully whippets look very aesthetically pleasing, so why have we kept on breeding the dogs whom had a single variant of the mutated gene? If we just stopped breeding on all of these, the bully whippet phenotype variant would be gone from the gene pool rather quickly, but there’s actually a logical reason why it has stuck around.

Like the greyhounds, whippets are also used as racing dogs, and can reach a velocity of 55km/h at its peak. They are not as popular to use for racing as the greyhounds, but there are still a lot of whippet racers out there, and this is where the mutation comes into play. The whippets who carry a single mutation of the gene are not only more muscular than the regular whippets, they are also significantly faster!

This pretty much means that they are much more likely to win races, and are therefore much more sought after by breeders who want to breed even faster dogs. It seems likely that a single dog once got this mutation and ended up winning a lot of races, leading to many offspring. The offspring who inherited the mutation would then most likely be very good runners, and also be used for breeding, and after a few generations the mutation is common in the gene pool.

For those who want a more advanced look at the mutation, here you go: The mutation in MSTN is a deletion in the third exon, which leads to a stop codon at amino acid 313 (the full length is 375 amino acids). When a single base pair is deleted, all the following genes will be misread by the ribosomes that read the RNA, since each amino acid is coded by a set of three bases.

There are three different stop codons, and if either of these (UAG, UAA, or UGA) are transcribed, the protein synthesis in terminated. This leads to the protein being prematurely finished, and in this case non-functional.

If the two last paragraphs didn’t make a lot of sense to you, but still sounded interesting, then I picking up a book about genetics, or reading the Wiki page about the genetic code. It's really interesting stuff if you have the patience to get into it!

Mendelian genetics of the bully whippet

If you end up breeding two dogs who both carry one set of the mutated gene, then one quarter of the litter will end up as bully whippets, half of them having a single set of the mutated gene, and one quarter of them won’t carry any mutated myostatin genes. This is pretty basic Mendelian genetics, so go read about that if you want to learn more about inheritance.

Anyway, bully whippets have way too much muscles, making them useless for racing. Luckily they have not had any reported negative side effects of the mutation except for muscle cramps, but that would also be because of a small sample size, so you might not want to go ahead and get yourself a bully whippet.

Get yourself a regular whippet instead. They’re pretty great! Image by @valth.

Other animals with the mutation

Whippets are not the only animals that can have this mutation, although it’s the only dog breed who have this mutation in the gene pool. The most famous example of a double set of mutation in this gene is from the cattle breed Belgian Blue, which are used for producing meat.

A Belgian Blue bull. Image by Flickr user agriflanders, posted with the Creative Commons Attribution 2.0 Generic license.

Belgian Blues and whippets are the only two animals that have this mutation in the regular gene pool, but scientists have been using CRISPR/Cas9 to inhibit the gene in other animals as well. Recently scientists inhibited it in both goats and rabbits, and both of these became more muscular after the inhibition. Some scientists believe that this gene and protein could be important in developing drugs or other treatments for muscle diseases such as muscular dystrophy, but we’re still far away from this.

Thanks for reading

I hope you found this post interesting, because I know I did! It was really cool to stumble upon this mutation when researching which dog breed to get, and I’m pretty sure that Wilma does not have it since I met both parents, and they did not look like they had a lot of muscles. But thanks for stopping by!

Most of the information about the MSTN mutation in whippets is from the scientific article "A Mutation in the Myostatin Gene Increases Muscle Mass and Enhances Racing Performance in Heterozygote Dogs" by Dana Mosher et al. The other sources are found directly in the text where they are relevant.

About @valth

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