Advancements in canine genetics
Henriëtte van der Zwan: Inqaba biotec : www.inqababiotic.co.za
Animal breeding has changed in latest years from a hobby to a science. Previously, selection of “the best” animals were mostly made upon phenotype. Today genetic tools are available to breeders aiding in select dogs based on genotype.
In 2005 the canine genome project was completed. DNA is made up of 4 base pairs: A, C, T and G, which are arranged in a specific order, and during this project the sequence of the base pairs in the dog genome was determined. A female Boxer called Tasha was used to compile the draft sequence of the dog genome. Later her genome sequence was compared to those of other dogs from various breeds. The genomes of species differ widely but breeds tend to be more than 99% similar. The sequence was uploaded into an international database that can be used by any genetic researcher around the world.
DNA consists of areas known as genes as well as non-coding or “junk” DNA areas. It is estimated that there are around 20 000 genes in the dog genome. To identify a gene as well as a mutation in the gene that cause a disorder or abnormality is like finding a telephone number without knowing the surname of a person. By comparing different dogs’ genotypes mutations (or difference between individuals) in certain genes could be identified and ultimately tests developed to eliminate these mutations from the breed.
During the genome project the “junk” DNA areas were also sequenced and by comparing different breeds and individuals genetic markers called Single Nucleotide Polymorphisms (SNPs) were identified. SNP markers are useful for identifying disease mutations, individual identification and breed identification. There are thousands of SNPs dispersed throughout the genome and they offer so much information that and applications.
One application of SNPs is breed identification. Certain SNPs are only found in certain breeds so a breed signature can be compiled for each breed. By comparing individuals to known reference samples in a database, scientists can tell whether a dog is a pure breed or if it is mixed. It can also tell the owner the percentages of each breed present in the mixed dog’s DNA. This is not only useful for owners who wish to know which breeds make up a mixed breed dog, but also for breed societies to guarantee that their breed is pure.
Technology advanced so rapidly that scientists are now able to quantify more complex traits, especially for production animals. As an example, in the dairy industry bulls can be tested to determine if their daughters will produce the same, more or less milk than the breed average, and thereby making selection of bulls much easier.
One similar test that looks very promising for dogs is the test for hip dysplasia. Unfortunately this test is currently still very expensive and not absolute. It will only tell you if a dog is more, or less likely than the breed average to develop HD. Another problem with HD is that the environment also plays a big role so a genetic test will never be 100% accurate. This test is not available in South Africa yet. Given the rapid advancements in genetic technology it may be possible to determine with a very high accuracy whether a dog will develop HD or not within the space of the next few years.
 Phenotype: Traits that are visible to the eye e.g. colour
 Genotype: The genetic make-up of the dog or what the genes look like
 Genome: The complete DNA of a species
 Gene: A short piece of DNA made up of base pairs that are arranged in a specific order. A gene has a specific function and if the order of the base pairs is altered, a disorder can occur.
 Mutation: A change in the sequence of the gene. This could lead to a disorder e.g. PRA or a new trait e.g. colour variations
 SNPs: Genetic markers where one nucleotide or base is substituted with another base.