. “The domestic dog is an extremely close relative of the gray wolf, differing from it by at most 0.2% of mtDNA sequence....

In comparison, the gray wolf differs from its closest wild relative, the coyote, by about 4% of mitochondrial DNA sequence.”

Robert K. Wayne, Ph.D.

“Molecular evolution of the dog family”
Theoretical and Applied Genetics

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 Click here for glossary of standard genetic terminology
and here to go to Index at the top of the page.


What is a Wolfdog?

A wolfdog is a cross between a gray wolf and a dog--what some refer to as a wolf hybrid. The term "hybrid", however, is used differently in the various scientific disciplines. For example, in horticulture, hybrids are formed by humans as crosses of different 'types' of plants; the term is used equally for crosses both among and within species. Conversely, in evolutionary biology, the term "hybrid" is used almost exclusively to describe offspring arising from a naturally-occurring cross between two separate and genetically distinct species. So one might recognize the potential for confusion arising from the use of the word "hybrid" when applied to a wolf/dog cross. It is more appropriate to refer to these animals as wolfdogs.

In 1993, the Smithsonian Institution and the American Society of Mammalogists reclassified the dog from its separate species designation of Canis familiaris to Canis lupus familiaris.  So, now, the Timber wolf (Canis lupus nubilus), the Mackenzie or Tundra wolf (Canis lupus occidentalis), the dog  (Canis lupus familiaris ), etc., fall under the genetic umbrella of the gray wolf: Canis lupus.


Background on DNA

Animals have two types of DNA, nuclear (nDNA) and mitochondrial (mtDNA). Nuclear DNA is found in the nucleus of a cell. The genes coded for by nDNA are responsible for external characteristics and for behavior, but they also have important regulatory functions inside the cells.  Mitochondrial DNA is separate and distinct from nDNA and is found in the mitochondria of the cell. The gene coding here is strictly regulatory and has little effect on external characteristics or behavior in comparison to nDNA.

Nuclear DNA occurs in the cell as tightly packed units called chromosomes and each cell has two copies of each chromosome. One pair of chromosomes are involved in sex-determination and are, therefore, called sex chromosomes; females have two X chromosomes and males have an X and a Y. The other chromosomes are called autosomes. All mammals have only one pair of sex chromosomes, but the number of autosomes varies according to species.

Genes are discrete pieces of DNA on the chromosomes that code for particular gene products, which are proteins. Slightly different forms of the same gene are referred to as alleles and each chromosome pair has two alleles; some alleles are dominant and are always expressed, while others are recessive and are only expressed when both alleles of a gene are recessive.

It is a myth that female (or male) genetics are stronger. Certain forms of genes (alleles) are dominant and these are expressed over recessive alleles, but dominant alleles do not occur in a higher frequency in males or females.  However, there are sex-linked genes (e.g., male pattern baldness in humans) and these recessive alleles--slightly different forms of the same gene--occur in nDNA, specifically on the X chromosome. Though we know much about sex-linked genes in humans, I personally know of no such studies that have been done on canids.

If you know of any new research that has been conducted on canid genetics or have anything to offer/counter, please reply or send via e-mail to me at Gwragedd Annwn as I would be interested in reading any scientific papers or hearing any comments.
 

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How is DNA Inherited?

Mitochondrial DNA comes solely from the female parent; the egg carries mitochondria as there is no room in the part of the sperm that fuses with the egg at fertilization. Here are a couple of examples to clarify how DNA is passed from parent to offspring:

It is important to bear in mind two things with regard to what has been said: (1) that the terms "wolf gene" and "dog gene" were used for simplicity rather than actually being two separate and distinct genes; and (2) that mtDNA is regulatory and is NOT coding for looks or temperament.  When a wolf and a dog mate, the outcome as far as looks are concerned is a crap shoot.  The DNA to look at in this case would be nuclear DNA, not mtDNA.


DNA: Wolves & Dogs

Mitochondrial DNA analysis, rather than nDNA analysis, is widely used to study populations of many animal species (including canids) because of its advantage over nDNA in that it does not recombine with other DNA as nuclear DNA does. The only way to conclusively determine (thru mtDNA) if a canid contains wolf content would be the presence of mtDNA restriction fragments specific to wolves. This is the root of the whole problem scientists are encountering when trying to differentiate between wolves and dogs. They are just too closely related, which is what led to the Society of Mammalogists and the Smithsonian Institution's taxonomical reclassification of dogs ( Canis lupus familiaris) as a subspecies of wolf (Canis lupus) in 1993 .

Many people erroneously believe that wolves and dogs are distinctly separate, one being 'black' and the other being 'white'. Throw in the wolfdog, and these same individuals see a completely different color: blue, green, purple, etc. However, Monty Sloan of Wolf Park put it simply: "there is no black and white in this issue, only shades of agouti gray."

 Click here for glossary of standard genetic terminology
and here to go to Index at the top of the page.

Wolf/Dog Genetic Research

Currently, scientists are having difficulties distinguishing definitively between wolves and dogs.  Robert K. Wayne and his colleagues are seriously pursuing this topic and things may or may not change in the future depending upon their ability to isolate the different alleles inherent in each animal.  Therein lies the crux of genetically differentiating between the wolf and the dog.

Below are some of the studies that have been conducted on this topic. The titles of the papers and their locations are provided, as well as the abstract or a short description. For further reading, click on the title and it will take you to the full paper.

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Can You I.D. Your Dog with DNA?
Ray Coppinger, Ph.D.
LGDA Doglog, Summer 1991

Through time there has been an infusion of unrelated genes, a sharing of mothers, so to speak, between species and between breeds. The wild animals we think of as distinct from one another, the purebred dogs we appreciate for their special form and behavior are not really unrelated. To a geneticist, the lines between the dog (Canis familiaris), the wolf (Canis lupus), or the coyote (Canis latrans) are indistinct because they are not true species, that is not reproductively isolated.

Molecular evolution of the dog family
Robert K. Wayne
Theoretical & Applied Genetics, June 1993, Vol. 9, No. 6.

Molecular genetic tools have been used to dissect the evolutionary relationships of the dog-like carnivores, revealing their place in the order Carnivora, the relationships of species within the Family Canidae, and the genetic exchange that occurs among conspecific populations. High rates of gene flow among populations within some species, such as the coyote and gray wolf, have suppressed genetic divergence, and where these species hybridize, large hybrid zones have been formed. In fact, the phenotype of the endangered American red wolf may be strongly influenced by hybridization with coyotes and gray wolves. Hybridization and habitat fragmentation greatly complicate plans to conserve the genetic diversity of wild canids.

Multiple and Ancient Origins of the Domestic Dog
Caries Vila, Peter Savolainen, Jesus E. Maldonado, Isabel R. Amorim, John E. Rice,
Rodney L. Honeycutt, Keith A. Crandall, Joakim Lundeberg, and Robert K. Wayne.
Science
,  Vol. 276, 13 June 1997.

Mitochondrial DNA control region sequences were analyzed from 162 wolves at 27 localities worldwide and from 140 domestic dogs representing 67 breeds. Sequences from both dogs and wolves showed considerable diversity and supported the hypothesis that wolves were the ancestors of dogs. Most dog sequences belonged to a divergent monophyletic clade sharing no sequences with wolves. The sequence divergence within this clade suggested that dogs originated more than 100,000 years before the present. Associations of dog haplotypes with other wolf lineages indicated episodes of admixture between wolves and dogs. Repeated genetic exchange between dog and wolf populations may have been an important source of variation for artificial selection.

Review of Wayne's Papers (Above)
Jody Haynes
(Full Review Included Below)

Wayne's recent papers on the genetics of dogs and wolves show, quite clearly, that "[d]ogs are gray wolves, despite their diversity in size and proportion" (Wayne, 1993). This review is intended to summarize the work of Wayne and his colleagues in trying to determine the phylogenetic relatedness of species within the Family Canidae, as well as the origin of the domestic dog and its relatedness to the gray wolf, Canis lupus.

Wayne's 1993 paper entitled “Molecular evolution of the dog family” (Theoretical and Applied Genetics, v. 9, or http://www.kc.net/~wolf2dog/wayne2.htm ) provides evidence—in the form of karyotypes (chromosome number and morphology) and nuclear and mitochondrial DNA markers—that there are four major phylogenetic divisions in the Family Canidae. The first of these divisions contains the wolf-like canids, which includes domestic dogs, gray wolves, coyotes, and jackals. Wayne then began to elucidate the genetic affinities shared by gray wolves and domestic dogs in the following statement: “The domestic dog is an extremely close relative of the gray wolf, differing from it by at most 0.2% of mtDNA sequence.... In comparison, the gray wolf differs from its closest wild relative, the coyote, by about 4% of mitochondrial DNA sequence.” Taken alone, these data suggest that gray wolves are 20 times more closely related to dogs than to coyotes.

Also in his 1993 paper, Wayne stated, “[t]he earliest remains of the domestic dog date from 10 to 15 thousand years ago...; the diversity of these remains suggests multiple domestication events at different times and places. Dogs may be derived from several different ancestral gray wolf populations, and many dog breeds and wild wolf populations must be analyzed in order to tease apart the genetic sources of the domestic dog gene pool.” Wayne further stated that “the wide variation in [the domestic dog's] adult morphology probably results from simple changes in developmental rate and timing” (Wayne, 1993). But the question is how this variation arose and how it has been maintained during the process of domestication.

To answer the first part of this question, Wayne and his colleagues set out to test the hypothesis that domestic dogs arose from the gray wolf at different times and places, as opposed to the competing hypotheses suggesting a “single origin” or a “single main divergence followed by numerous subsequent intermixing events.” To do this, Wayne chose to analyze rapidly evolving mtDNA sequences.

Wayne et al.'s 1997 paper (Science, v. 276, or http://www.kc.net/~wolf2dog/wayne1.htm ) summarized their mtDNA analyses, stating that several different methods of phylogenetic analysis supported the grouping of various dog mtDNA haplotypes into four distinct clades. (Note: A clade is a purported monophyletic group in which all members share a single common ancestor at some unidentified point in the past.) Figure 2 in this latter paper represents a graphical depiction of hypothetical phylogenetic relationships of mtDNA haplotypes from wolves and dogs. This ‘gene tree’ suggests that the mitochondria of the dogs listed in clades 2 and 4 are more closely related to the mitochondria of wolves than they are to the mitochondria of the dogs in clades 1 and 3. If these analyses of mtDNA haplotypes represented the genetics of the whole organisms, this figure would suggest that dogs are polyphyletic, which would mean that the term “dog” would no longer represent a genetically coherent group of organisms. However, a single gene tree may not represent the true genetic affinities of the organisms involved (dog breeds, wolf subspecies, etc.).

Later in this paper, Wayne et al. cited a robust analysis of mtDNA control region sequences that strongly rejected the monophyly of all dog haplotypes (P = 0.0004). This result suggests that all dog mtDNA haplotypes did not arise from a single divergence event (i.e., are not monophyletic), thereby rejecting the “single origin” hypothesis. In other words, just because Wayne's research focuses primarily on mtDNA—and not on individual nDNA or on the whole organisms—we cannot completely ignore the possible explanations for the cause of the observed distribution of mitochondrial haplotypes into four clades or the rejection of monophyly among all dog mtDNA haplotypes.

Wayne et al. (1999) nicely summarized this earlier work by stating that the clustering of dog haplotypes into four distinct clades “suggests that either wolves were domesticated in several places and at different times or that there was one domestication event followed by several episodes of admixture between dogs and wolves.” Wayne et al. continued by stating "[w]hichever the case, the results imply that dogs have a diverse origin involving more than one wolf population"; Wayne et al. then concluded by stating "[i]n conclusion, the domestic dog is a genetically diverse species that likely originated from wolf populations existing in different places and at different times."

To sum up, Wayne's original “different times and places” hypothesis has not been rejected. Furthermore, more work needs to be done to differentiate this hypothesis from the “single main divergence, secondary intermixing” hypothesis.

The Origin of Dogs: Running With the Wolves
Virginia Morell
Science,  Vol. 276,  13 June 1997

An international team of geneticists and evolutionary biologists reveals on page 1687 of this issue [that] all of today's breeds had only one canine forebear: the wolf. What's more, the team, lead by Robert Wayne of the University of California, Los Angeles, says that although humans tamed members of that lone progenitor species at least twice, domestication was apparently a relatively rare event, requiring special skill. The researchers also say that the first transformation from wolf to dog may have happened more than 100,000 years ago--long before the 14,000-year date archaeologists typically assign to Fido's domestication. Many biologists remain skeptical about the date, but they are impressed by the genetic study, the largest of its kind for the dog. "That's absolutely great; it's first-rate," says Stephen O'Brien, a geneticist and chief of the Laboratory of Genomic Diversity at the National Cancer Institute in Frederick, Maryland, who has done similar genetic studies of wild and domestic cats. "He has confirmed genetically what most zoologists have believed for a long time," adds David Mech, a wolf expert with the Department of the Interior in St. Paul, Minnesota, "and that is that the dog is a domesticated wolf."

 Click here for glossary of standard genetic terminology
and here to go to Index at the top of the page.


Researchers in Canid Genetics

Below is a list of the various researchers involved in Canidae genetics in some form or another. Most of this information was obtained from the American Kennel Club at http://www.akc.org/conf.htm .  However, there are links provided in each paragraph, which will take you directly to the home page of that particular business, department, or school.

Genetic Diversity and Evolutionary History of the Dog
Robert K. Wayne; Department of Biology, University of California at Los Angeles, Los Angeles, California U.S.A. 90095-1606.

C.A.T.S. On Dogs: Optimization and Polymorphism Screening Of Comparative Anchor Tagged Sequences in Domestic Dogs and Wild Canids
L.A. Lyons, J.S. Kehler, and S.J. O'Brien; Laboratory of Genomic Diversity, National
Center Institute, Frederick Cancer Research and Development Center, Frederick, MD.

Genetic Variation Within and Between Canidae Species
M. Fredholm; The Royal Veterinary and Agricultural University, Copenhagen, Denmark.

DNA Profile Testing of Vizslas: Breed Purity and Registry Identification
W.F. Gergits and N.J. Casna; Therion Corporation, Troy, NY 12180.

Within and Between Genetic Variation in 16 Dogs Breeds
F. Lingaas(1), T. Aarskaug(2), and P.-E. Sundgren(3); (1)Department of Animal Genetics and Norwegian Kennel Club , (2)Department of Animal Genetics, Norwegian College of Veterinary Medicine, Oslo, Norway, (3)Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala, Sweden.

The Evolving Canine Map
C. S. Mellersh, A. A. Langston, G.M. Acland, M. A. Fleming, K. Ray, N. A. Weigand, L. V. Francisco, M. Gibbs, G. D. Aguirre, and E. A. Ostrander; Clinical Research Division-M318, Fred Hutchinson Cancer Research Center, Seattle WA.

DogMap - An International collaboration towards a low resolution canine genetic marker map. The DogMap Consortium.
G. Dolf; Institute of Animal Breeding, University of Berne, Berne, Switzerland.

Chromosome Paints and their Uses
C.F. Langford(1), M.Breen(2), H.F. Dickens(2), N.G. Holmes(2), M.M. Binns(2), and N.P. Carter(1): (1) The Sanger Centre, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA, U.K. and (2) Animal Health Trust, P.O. BOX 5, Newmarket, Suffolk, CB8 7DW, U.K.

Canine FISH Cytogenetics
M.Breen(1), C.F. Langford(2), H.F. Dickens(1), N.G. Holmes(1), N.P. Carter(2), R. Thomas(3), N. Suter(3) and M.M. Binns(1): (1) Animal Health Trust, P.O. BOX 5, Newmarket, Suffolk, CB8 7DW, U.K.; (2) The Sanger Centre, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA, U.K.; and (3) Department of Biochemistry, University of Leicester, U.K.


  More Canid Genetics Sites:

Intro to Canine Genetics
The Dog Genome Project
The Wolfdogs Resource
Genentech Inc.
Canine Genetic Resource
DNA and Your Dog
FHCRC Dog Genome Project
Wolves: DNA Pawprinting
Mammalian Genetics and Disease Mapping
Genetic Linkage Analysis in Dogs



 
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