More on the evolution of dogs
- Another new study on the domestication and genetics of dogs was
published this morning in PLoS Biology, for those on the List
following this issue:
Canine Morphology: Hunting for Genes and Tracking Mutations
http://tinyurl.com/y9duoyf (open access).
The paper covers major issues in studies of mutations that go far
beyond the canine-domestication problem.
Plain text of the summary and introduction only below.
Canine Morphology: Hunting for Genes and Tracking Mutation
Abigail L. Shearin1,2, Elaine A. Ostrander1*
1 National Human Genome Research Institute, National Institutes of
Health, Bethesda, Maryland, United States of America, 2 University of
Pennsylvania School of Veterinary Medicine, Philadelphia,
Pennsylvania, United States of America
Published: March 2, 2010
As a result of domestication, selection for desirable phenotypes, and
breed propagation, the domestic dog is unmatched in its diversity as a
land mammal. Exhibiting extraordinary levels of both interbreed
heterogeneity and intrabreed homogeneity, evidenced in part by the
extensive linkage disequilibrium observed in many breeds, the dog
provides an as-yet unrealized opportunity to uncover the molecular
mechanisms that govern natural variation across mammalian species. We
herein discuss recent advances in canine genomics that have made
exploration of genetic mechanisms controlling breed-specific
differences possible. We consider some examples where molecular
mechanisms controlling simple traits have been uncovered. Finally, we
reveal how combinations of genes produce complex phenotypes that can
be revealed through studies of dog breeds featuring specific traits.
As Darwin himself noted, the domestic dog displays a remarkable level
of phenotypic diversity , and it is arguably the most
morphologically variable land mammal on the earth today. Dogs can be
big or small, tall or short, and display extremes of variation in
terms of coat color and texture, skull shape and size, leg length and
width, and a host of other traits (Figure 1). How this variation
developed and is maintained within breeds intrigues both scientists
– and the lay public alike.
There are over 300 dog breeds identified worldwide, with nearly 170
recognized in the United States by the American Kennel Club (AKC) .
All domestic dog breeds are members of the same species, Canis
familiaris, and possess a 2.8 Gb genome featuring 38 autosomes and the
sex chromosomes, similar in size to the 3 Gb human genome. Dogs of any
breed can, for the most part, be crossed to produce fertile offspring.
Breeds were developed largely during the Victorian era, with special
selection for both morphologic traits based on size, proportion, coat,
etc., as well as behavior. To be a registered member of a breed, both
of a dog's parents have to be registered members of the same breed,
and their parents in turn must be registered members of the breed.
Thus, each breed is effectively a closed breeding population that
offers many statistical advantages for doing genetics beyond what can
be done in studies of human populations .
In this essay we consider some of the features of the canine genome
relevant for successful studies of selected traits. We discuss current
hypotheses regarding the development and maintenance of genetic
variation in dogs today. We consider examples in which identified
genes account for unique, and sometimes complex, phenotypes. Finally,
we consider the implications of these findings for studies of true
complex traits, such as those associated with behavioral genetics.