I'm not a dog person. I'm a cat person. However, the sight hounds have always fascinated me. They are some pretty stunning creatures. So, while doing a little research today, I came across this older article and thought I would share.
Whippets are like small greyhounds. The fastest of them can top out at 40 mph. There is a not-unique mutation in them though. And that mutation brings up an interesting point that a lot of people miss.
The mutation is in the myostatin (MSTN) gene that develops muscles. Here's where it gets interesting.
If you get a dog that has one of these mutated genes (from either mom or dad), then you get one of the fastest Whippets. That dog could easily be a race champion. The mutation basically increases the amount of muscles in the dog. So, no mutated genes and you get a dog with normal muscles. One mutated gene and you get impressive muscles. What happens when you get two mutated genes?
You end of with freakishly large muscles that actually cause some significant problems and constant threat of massive cramping. Dogs with two genes are slower than dogs with one gene.
Here's a normal Whippet. Notice the sleek shoulders and hips.
Gorgeous animal right?
Here's a so-called 'bully whippet' with that is homozygous for the mutated gene.
Yes, those two dogs are the same breed.
This is a really neat concept and one that is actually quite common. The heterozygous condition (one mutated gene and one non-mutated gene) is more fit than either of the two homozygous conditions (two mutated genes or two non-mutated genes) in the same environment.
Can anyone think of another case where, in some environment, the heterozygous condition is more fit than either homozygous condition? Yes, you in the back.
Yep, sickle cell anemia. In environments with malaria, the heterozygous condition is more fit than either homozygous condition.
A similar case can be found in my preferred species of discussion (Felis catus). the tailless condition of the Manx breed is due to a heterozygous condition. The tailless condition is dominant, but a homozygous dominant cat never survives. They are always stillborn. In a sense, there can be no pure-bred Manx cats.
Why is this cool, it takes care of one of those things that some people complain about in evolution. That is diversity. If everything moves towards maximum fitness, then why does diversity exist?
Well, that's not a bad question and there are two answers. The first is that what is 'fit' changes based on the environment. If the environment does not contain malaria, then a homozygous non-sickle cell person is most fit. If the environment contains malaria, then a heterozygous person is most fit.
Since a cross between two heterozygotes can produce either homozygous condition or the heterozygous condition, then diversity in the population will remain higher than if one of the dominant conditions were most fit.
The other answer is that the environment can change (and does frequently). Take a look at the Galapagos finches and the change in morphology between droughts and rainy seasons. Note that if one environment persisted for a significant amount of time, then the most fit condition could become fixed in the population (if the most fit condition wasn't the heterozygote).