The Dog Genome Project: Principles and Goals
By Jasper Rine
The dog genome project is a collaborative study involving scientists at the University of California, The University of Oregon, and the Fred Hutchinson Cancer Research Center aimed at producing a map of all of the chromosomes in dogs, which can be used to map the genes causing disease and those genes controlling morphology and behavior. Different dog breeds are distinguished by varieties of morphologies and behaviors that exceed the range of variation in any other species on earth. Dog genetics offers the hope of discovering the genetic basis of both mammalian development and behavior.
This project brings together for the first time the two greatest ideas in 19th century biology, the discovery of Charles Darwin showing that evolution results from selection and the discovery by Gregor Mendel of the laws of genetics. The fundamental lesson from the work of Mendel is how to recognize the existence of genes. Mendel taught us that by crossing two individuals that differ in a trait and observing how that trait segregates in subsequent generations, it is possible to discover the existence of and certain properties of the gene responsible for that trait. Because members of the same species are usually quite similar, Mendel concentrated on the differences that plant breeders had recognized in peas and was limited to the study of a relatively small number of differences.
Darwin was the first to recognize that natural selection, commonly referred to as survival of the fittest, was the driving force of evolution. Minor differences arise between individuals in a species through natural processes of mutation. Most mutations are harmful and decrease the chance of survival. However, for those few mutations that cause a favorable change that enhance survival, the mutations will spread throughout the population due to the enhanced survival of the individuals with the mutation. The accumulation of mutations over time leads to the creation of new species.
In theory, one could discover the genes responsible for the differences between breeds if it were possible to cross two members of a different species and observe the segregation of the train in the offspring. For example, the genes controlling wing length in birds would be recognized in the offspring of a cross between condors and hummingbirds. Similarly, the genes controlling the length of the neck in mammals would segregate in a cross between giraffes and warthogs. Of course, the definition of species precludes such an experiment due to the reproductive isolation that separates different species. Nevertheless, if such differences were to exist in a single species, the genes responsible for these differences could be identified.
Darwin also recognized that natural selection in nature was similar to the artificial selection practiced by breeders to improve the stature or performance of agriculturally important species. Because of the stronger selection pressure that can be exerted over a shorter period of time by breeders, artificial selection can result in differences of such magnitude between subgroups in a species than would normally occur between members of a different species. Indeed, the remarkable variety exhibited by many dog breeds has been produced in approximately 150 years by dog breeders.
There are on the order of 150 recognized dog breeds in the world and collectively these breeds represent an ongoing experiment in evolution. By careful observation and selective breeding, dog breeders have created breeds with astonishing breed-specific differences. The mass of Pekingese and Irish Wolfhounds differ by fifty-fold, and the behavior of Doberman Pinschers and Golden Retrievers could hardly be more different. Yet remarkably, a dog of any breed can be crossed to a dog of any other breed and produce viable and fertile offspring. Moreover, dogs are inter-fertile with wolves, jackals, and coyotes as well. Thus, in dogs we have the opportunity to study the fruits of selection with the scientific power provided by the laws of genetics to sort out the genetic basis of mammalian morphology and behavior, and to gain experimental access to the evolutionary process. There is no other comparable opportunity in biology.
A second goal of the dog genome project is to develop a map that will be useful to the entire scientific community for the purpose of mapping genes causing inherited disease in dogs. It is widely recognized that in many pedigreed dog lines diseases run in families. These diseases include cancer, epilepsy, retinal degeneration, bleeding disorders, skeletal malformations and a host of others. Much of the revolution in human molecular medicine has been catalyzed by the development of the human genetic map, which has allowed genes responsible for human genetic disease to be isolated. The isolation of these genes has provided highly accurate diagnosis of many diseases well before the appearance of the first symptoms. In many cases, insight into the molecular basis of the disease is leading to the development of new therapeutic compounds, and the promise of gene therapy has already been achieved in one case. None of this progress in human medicine would have been possible without a high quality genetic map. The map being produced by the dog genome project will catalyze a similar explosion in veterinary medicine and will allow more effective breeding practices to eliminate many genetic diseases from breeds currently afflicted. It is important to keep in mind that a genetic map grows in utility as more people contribute to it and benefit from it. Therefore it is the practice of the dog genome project to make all research results available to the scientific community well prior to traditional publication through electronic publication on the World-Wide Web.
For those of you like myself who read these articles with a dictionary: genome -- "one complete haploid set of chromosomes of an organism;" haploid -- "having the full number of chromosomes normally occurring in the mature germ cell or half the number of the usual somatic cell;" morphology -- "the branch of biology that deals with the form and structure of animals and plants."
Thanks to Laurie Brooke Adams for cruising the Internet newsgroup rec.pets.dogs for tidbits like this, and to Mellissa DeMille for having posted it on the net and obtaining permission to reprint from the author.