Whippets, Bullies, and Genetics

Nov 04 2011 Published by under Uncategorized

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?

Super dog!

Well... no.

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.

from: http://dogbreedsinfo.org/Whippet.html

Gorgeous animal right?

Here's a so-called 'bully whippet' with that is homozygous for the mutated gene.

from http://www.dailymail.co.uk/news/article-467985/Meet-Incredible-Hulk-Hounds.html

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).

Here's the actual research on the muscles in whippets.

 

23 responses so far

  • the bully whippet looks like it might snap in half if it takes a turn to sharply.

  • Joe G says:

    Chapter IV of prominent geneticist Giuseppe Sermonti's book Why is a Fly Not a Horse? is titled "Wobbling Stability". In that chapter he discusses what I have been talking about in other threads- that populations oscillate. The following is what he has to say which is based on thorough scientific investigation:

    Sexuality has brought joy to the world, to the world of the wild beasts, and to the world of flowers, but it has brought an end to evolution. In the lineages of living beings, whenever absent-minded Venus has taken the upper hand, forms have forgotten to make progress. It is only the husbandman that has improved strains, and he has done so by bullying, enslaving, and segregating. All these methods, of course, have made for sad, alienated animals, but they have not resulted in new species. Left to themselves, domesticated breeds would either die out or revert to the wild state—scarcely a commendable model for nature’s progress.

    (snip a few paragraphs on peppered moths)

    Natural Selection, which indeed occurs in nature (as Bishop Wilberforce, too, was perfectly aware), mainly has the effect of maintaining equilibrium and stability. It eliminates all those that dare depart from the type—the eccentrics and the adventurers and the marginal sort. It is ever adjusting populations, but it does so in each case by bringing them back to the norm. We read in the textbooks that, when environmental conditions change, the selection process may produce a shift in a population’s mean values, by a process known as adaptation. If the climate turns very cold, the cold-adapted beings are favored relative to others.; if it becomes windy, the wind blows away those that are most exposed; if an illness breaks out, those in questionable health will be lost. But all these artful guiles serve their purpose only until the clouds blow away. The species, in fact, is an organic entity, a typical form, which may deviate only to return to the furrow of its destiny; it may wander from the band only to find its proper place by returning to the gang.

    Everything that disassembles, upsets proportions or becomes distorted in any way is sooner or later brought back to the type. There has been a tendency to confuse fleeting adjustments with grand destinies, minor shrewdness with signs of the times.

    It is true that species may lose something on the way—the mole its eyes, say, and the succulent plant its leaves, never to recover them again. But here we are dealing with unhappy, mutilated species, at the margins of their area of distribution—the extreme and the specialized. These are species with no future; they are not pioneers, but prisoners in nature’s penitentiary.

    Just sayin'...

  • Joe G says:

    If everything moves towards maximum fitness, then why does diversity exist?

    Everything doesn't move towards a maximum fitness. Everything may move (or not) but fitness depends on more than one thing- as you said environments change, meaning pressures change. And that is only one variable.

    Sometimes behavioural changes are the only way to get by. That means if I am "a homozygous non-sickle cell person" in Africa, I can get mosquito netting, repellent and one of those tennis raquet bug zappers, thereby making the (fitness) odds even.

  • EEGiorgi says:

    You're both missing about one century of population genetic studies. The discussion you guys are having makes no sense whatsoever without knowing the work of JBS Haldane, Motoo Kimura, and Luigi Cavalli-Sforza.

  • EE,

    Is my explanation fundamentally wrong to the point where it would be inappropriate to teach to 9th grade students? If so, then how would I best explain this at that level?

    Or is just the conclusion regarding diversity?

    Or is incomplete?

    Like I said, I'm coming from trying to explain this to people with little or no science background and math limited to Algebra 1 or lower.

    Thanks

    P.S. I've got that Kimura book on my wish list.

  • Jim Thomerson says:

    Hardy-Weinberg, at least, is at Algebra I level. Another example is silver foxes, where homozygous silver is lethal. I have posed the situation where a businessman wants to start a silver fox business raising them free range on a large island. He stocks the island with silver foxes, has them fed regularly, and comes back in a few years. What does he find? I also made up a lab exercise about selection, using beans for genes, which mimics this situation.

  • EEGiorgi says:

    Kevin, the concept that's fundamentally wrong is that "every trait is selected for." I just posted about Haldane's dilemma and how he postulated a model in which every trait was selected for. He concluded that only one trait at the time could be selected and it took 300 generations for the trait to get fixed. Obviously, this doesn't explain the amount of diversity we observe today. Kimura elaborated Haldane's theory and came to the conclusion that it was the opposite, that all mutations are neutral (have no effect) and they get fixed just because of genetic drift (basically, the fact that some individuals reproduce and others don't -- this is NOT selection pressure!). If you formulate a mathematical model for each position, you see that each extreme is incomplete. Please see my post here:
    http://chimerasthebooks.blogspot.com/2011/11/haldanes-dilemma.html
    where I try to explain that most traits are not under selection pressure, but that selection pressure does pick some on a occasional sweeps (like a seasonal virus, for example).
    Cavalli-Sforza's papers are also most interesting because they retrace migrations with the change in genetic alleles, again proving that most alleles got fixed just because people moved and populations split. It's hard to condense all this in a post, but I'll be happy to answer any questions you have and engage in a longer conversation. These concepts are important and we need to explain them to the new generations! But if we are not accurate in explaining these concepts we risk of motivating more those who, sadly, don't believe in evolution.

  • Interesting, I think I understand this at a decent level... thought the non-selection of multiple traits is new.

    That's one of those things that I never really considered, because, at the level I normally teach at, we must consider traits in isolation. Heck concept of a dihybrid cross blows their minds.

    I agree with the mostly nuetral, provided that caveat is mostly. I can think of at least one trait that provides a survival advantage, but not a reproductive advantage because it only kicks in well past normal reproductive age.

    Unless a gene is fatal, then it would be rarely selected against.

    Kimura seems to explain why recessive genes seem to be fixed in the population.

    I guess one question is why can only one trait be selected for or against at a time? This seems like a pretty radical statement considering that a) all organisms have hundreds of genes and many alleles per gene and b) that the organism is a package deal. My trait of near0sightedness cannot be separated from my trait of AB+ blood type and my height.

    Sure, each trait would be beneficial or detrimental in specific circumstance and the circumstances for one trait to be be beneficial may have nothing to do with another trait or circumstances... so why just one trait at a time?

  • EEGiorgi says:

    Oh, and with regards to your question about heterozygosity being fitter: first of all, why shouldn't heterozygosity being fitter? Fitter or less fit are concepts we assign a posteriori. So, let's use the term with extreme care. Nature doesn't have intentions. Having said that, heterozygosity is EXTREMELY important when it comes to the immune system. In fact, one thing that I believe we can say with sufficient certainty is that heterozygosity in the MHC complex of genes has over time been selected for. MHC molecules are responsible for presenting antigens to T-cells, the sentinels of our immune system. Now, antigens come in wide varieties, hence the more variety we have in MHC molecules, the better we are at recognizing viruses and infections. So, that's one region of our genome where heterozygous individuals have a definite advantage.

  • EEGiorgi says:

    > so why just one trait at a time?

    That was Haldane's conclusion in the 1957 paper. The idea is that if there's strong pressure on one trait, others get inevitably lost.

    But again, that is an extreme. In real life you don't see extreme pressure constant over time on one trait in particular. You see sweeps.

    Now, the other thing to keep in mind is that when chromosomes recombine they do not do so at random. Many regions in the genome are linked together, something that is measured through Hardy-Weinberg equilibrium (Jim's comment, above), whether the equilibrium is met or not. Today we know that the human genome is divided in "haplotype blocks" which tend to get inherited together and, interestingly, they have different patterns across different racial groups. If two alleles are in the same block and one is under selection pressure, the second allele will get fixed just because of its correlation with the first one.

    • Joe G says:

      There was a recent experiment involving fruit flies that put Haldane to the test:

      Genome-wide analysis of a long-term evolution experiment with Drosophila:

      Abstract

      Experimental evolution systems allow the genomic study of adaptation, and so far this has been done primarily in asexual systems with small genomes, such as bacteria and yeast1, 2, 3. Here we present whole-genome resequencing data from Drosophila melanogaster populations that have experienced over 600 generations of laboratory selection for accelerated development. Flies in these selected populations develop from egg to adult ~20% faster than flies of ancestral control populations, and have evolved a number of other correlated phenotypes. On the basis of 688,520 intermediate-frequency, high-quality single nucleotide polymorphisms, we identify several dozen genomic regions that show strong allele frequency differentiation between a pooled sample of five replicate populations selected for accelerated development and pooled controls. On the basis of resequencing data from a single replicate population with accelerated development, as well as single nucleotide polymorphism data from individual flies from each replicate population, we infer little allele frequency differentiation between replicate populations within a selection treatment. Signatures of selection are qualitatively different than what has been observed in asexual species; in our sexual populations, adaptation is not associated with ‘classic’ sweeps whereby newly arising, unconditionally advantageous mutations become fixed. More parsimonious explanations include ‘incomplete’ sweep models, in which mutations have not had enough time to fix, and ‘soft’ sweep models, in which selection acts on pre-existing, common genetic variants. We conclude that, at least for life history characters such as development time, unconditionally advantageous alleles rarely arise, are associated with small net fitness gains or cannot fix because selection coefficients change over time.

  • Jim Thomerson says:

    Simple Darwinian fitness is a measure of how successfully an individual raises offspring to sexual maturity. I suppose one has to wait and see. There are many examples of stabilizing selection, where average individuals have higher fitness than extreme individuals. Generally, populations are composed largely of individuals close to average, which suggests that those individuals are more fit. Average individuals tend to be more heterozygous than extreme individuals. So a population of average individuals will continue to produce new generations including extreme individuals. Hardy-Weinberg tells us that, under H-W conditions, the most individuals heterozygous for a particular pair of alleles occurs when the frequencies of the two alleles in the population are equal.

    • Joe G says:

      OK if the average is the most fit then what does that say for the theory of evolution?

      IOW, how can populations evolve if they basically stay the same?

  • Kevin, EE, and Jim, thank you guys for some great debating. I've got some stuff to look up now, the discussion between you three has been nothing short of enlightening.

  • Jim Thomerson says:

    Let's suppose a population has lived under similar conditions for many generations. When we examine the population, we find that most of the individuals are near average. Is that not what one would expect? What we are talking about here is called stabilizing selection. I suspect stabilizing selection is perhaps the most common form of selection. Bumpus with his study of house sparrows who survived the storm, was probably the first published example.

    Suppose there is a change in the situation and the average individuals are no longer highly fit, but individuals toward one extreme are now more fit. Over generations we would expect the former extreme to become more and more common until it is the new average.

    There is also differential or divisive selection, where both extremes are more fit than the average. This should lead to a bimodal distribution rather than the usual bell shaped curve. I think this has been found is some of Galapagos finch studies. I think differences between human males and human females are a result of, or, perhaps, subject to, differential selection. I don't think an individual in the middle , between male and female averages, would be expected to have high fitness. There should be data in the literature on reproductive success of transgender folks.

    • Joe G says:

      There is at least one paper on that- the selection pressure is on the average and the two extremes were then "split" (as if they had be geographically separated)- the paper was pointing out that it is unnecessary to physically move in order to get a split in the population that would lead to a divergence.

  • OgreMkV says:

    I didn't realize you were talking about sexual characters until you said transgender.

    I was thinking size, muscles, etc and thinking, well, there's a big range, but it's not bimodal.

    AFAIK, most of the transgender are chromosome malfunctions and they would have serious impediments to reproducing anyway... which supports your point.

  • Jim Thomerson says:

    I think you are mistaken that size, muscle mass, etc. do not show a bimodal distribution. When averages are significantly different between the two sexes, there well may be some overlap in the distributions. Even so, the distribution is still bimodal.
    http://en.wikipedia.org/wiki/Sex_differences_in_humans

    I misused transgender, I meant either a male or a female at the average for the pooled curves for both sexes. A female taller than most females, or a male, of the same height, shorter than most males, for example.

  • OgreMkV says:

    OK, so you meant what I initially thought.

    But is the current human situation trending toward bimodal or is it trending toward the middle?

    Not that it actually matters, but it's an interesting question.

  • Jim Thomerson says:

    We see in the newspapers that taller men tend to be more successful in life. I read that Holland now has the tallest population, passing the USA. There was Gould Natural History column on sexual dimorphism in size. Large female, small male species have promiscuous females. Large male, small female species have promiscuous males, and the rate is predictable from the size relationship. As I recall, human males, on average, are supposed to breed with 1.28 females.

  • First, this is highly depressing... I'm below average.

    Second, I have recently moved from one location, where I was among the tallest to a new location where I am very average in height. My personal success has been much higher here than there. Not that actually means anything...

  • Jim Thomerson says:

    Statistics are about the group. So it is OK to go against them, as an individual, if you can manage it. Lottery winners do it all the time.

  • Bettina says:

    This may have nothing to do with your article, but I do have a question for which I can't seem to find an answer. I have a Whippet. Three and a half years old from rescue. He is 12 pounds, 13 inches at the shoulders. He is not a mix. Can you tell me what kind of Whippet he may be? Are there miniatures? Or is mine a special runt of the litter? I am very curious. Jackson is the sweetest, gentlest of creatures with a very high speed at full giat and yet very small. Any information would be appreciated. Thank you.