Variation in dog coats

October 2, 2009 • 7:55 am

by Matthew Cobb

This blog normally (and rightly) gives pride of place to cats, but this post will be about dogs. I trust Jerry will forgive me when he returns.

Hidden away in the same issue of Science that deals with Ardi, there’s an article by a host of researchers from the US and France (you’ll need a subscription to get past the abstract), looking at the genetics of dog coat variation. Amazingly, it turns out that most of the massive range in coat phenotypes we can see between “pure breeds” and mongrels can be accounted for by mutations in just three genes. (If I were one of the authors, I’d be pretty peeved – all the media attention will be focused on Ardi; in a “normal” week, they could be sure of making the TV, press and radio…)

The authors studied three characteristics of the canine coat: (i) the presence or absence of “furnishings” (growth pattern marked by a moustache and eyebrows seenin wire-haired dogs); (ii) hair length; and (iii) the presence or absence of curl. To find the genetic bases of these characters, they created three genome-wide single-nucleotide polymorphism (SNP) data sets, based on a) 96 dachshunds showing three coat varieties (wire-haired with furnishings, smooth, and long-haired without furnishings); b) 76 Portuguese water dogs showing the curl phenotype and c)  903 dogs from 80 breeds representing a wide variety of phenotypes.

They found that variability in three genes, coding for R-spondin–2, fibroblast growth factor–5, and keratin-71, accounts for most of the different kind of coats that can be observed (“these three mutations in various combinations explain the observed pelage phenotype of 95% of dogs sampled”) . They summarise their findings in the following figure:

326_150_F3

Interestingly, they conclude “None of the mutations we observed were found in three gray wolves or the short-haired dogs, indicating that short-haired dogs carry the ancestral alleles (table S1). Our finding of identical haplotypes surrounding the variants in all dogs displaying the same coat type suggests that a single mutation occurred for each trait and was transferred multiple times to different breeds through hybridization.”

However, although they open their article by pointing out that dogs and humans have lived together for around 15,000 years, they point out in their conclusion that dog “breeds” are an incredibly recent invention – less than 200 years. Inother words, in a couple of hundred year, artificial selection on just three genes has produced an incredibly variety of phenotypes. Furthermore, that selection may have focused on different characters, such as aggressivity or size, the genes for which may be linked to the coat genes. They conclude, “Consequently, in domesticated species, the appearance of phenotypic complexity can be created through combinations of genes of major effect, providing a pathway for rapid evolution that is unparalleled in natural systems.”

This, of course, was also Darwin’s insight (although he did not put it in these terms). Artificial selection by 19th century breeders provided him with the key to understanding natural selection as the force that could generate apparently directed evolutionary change. And that is a much more powerful explanation than anything the creationists can come up with.

26 thoughts on “Variation in dog coats

      1. CORRECTION:

        “Pride” to “cats?”

        Srsly, Matthew, leave the humor to me!

        (Sorry I barked up the wrong tree.)

  1. The linking of disparate phenotype traits to a single gene or multiple gene sets appears to be a nightmare to deduce. Whether artificial or natural selection, a small change can have far reaching changes that will require thousands of studies to understand even one entire genome. I guess this means that the science of biology does not disappear any time soon due to lack of work.

    1. Indeed odd, to apparently come from the side of science yet refer at the end to evolution as the flickering light of a hand-held candle!

  2. Thanks so much for this post, I actually work on coat color and structure in other mammals and am currently carrying out a project on fgf5. What is even more interesting is that fgf5 is reported as responsible for the “long hair” phenotypes in many other mammals (cat, mouse, goat, sheep and more)

    1. You’re absolutely right, Glen. In fact, I used precisely that analogy in a lecture to 600 First Year students this morning – if evolution were to be tested in a court of law, the DNA evidence alone would be enough to return a verdict of “proven”!

      Matthew

  3. Are there no examples of phenotypes with a mutation only in keratin-71?

    Perhaps it would be short and curly (identical to F)?

    And how about coat color and patterning? Is variation in the genes coding for that also a recent occurrence? Any studies on that?

    1. I was wondering that too… there is no – – +

      I have a shepherd-looking dog with sort of medium fur… (and an all black tongue).

  4. Heh – I saw a talk by Elaine Ostrander, presenting this data (over the phone, since she couldn’t make it in person!) at the ISDB in Edinburgh last month. It was a fun talk.

    1. There is no such thing as KINDs. Ken Ham is an ignorant liar and his web site is nothing but ignorant garbage.

  5. Perfect that the current thread is about dogs since I need a segue to wolves. I hope everyone is or will have a chance to watch Ken Burns’ National Parks series. The last episode, that I’m watching now, has a great segment about Adolph Murie’s studies of the wolf while a Park Service agent, that led to protection of the species within the parks.

    The whole series has been full of examples of the results of efforts of single individuals, and has also been commendable in playing up the age of the earth here and there while avoiding any hint of creationary blather. An excellent production!

  6. Dog breeds are less than 200 years old?

    Yeah, right. The name ‘King Charles Spaniel’ ought to suggest a doubt or two about this. Or Shakespeare’s Macbeth:

    “Ay, in the catalogue ye go for men,
    as hounds and greyhounds, mongrels, spaniels, curs, shoughs, water-rugs, and demi-wolves are clipt all by the name of dogs.”

    Major breeds like greyhounds, wolfhounds, mastiffs, and spaniels all go back much further than 200 years, though of course the modern pedigree breeds are not identical to their ancestors.

  7. The list there doesn’t have KRT71 “by itself” (-,-,+).

    One wonders if it only occurs with at least one of the other two, or if it just didn’t contribute enough to the variation (perhaps because it’s rare).

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