Understanding the Dog's Genetic Size Facilitates Planning Individual Care and Weight Control

MyDogDNA has now added four new size associated genetic markers called GHR1, GHR2, HMGA2, STC2and a test for breed-defining chondrodysplasia to the test panel. These markers, together with the previously reported size associated markers in IGF1 and IGF1R give more information on the dog size, supporting finer prediction of the genetic size of a dog.

Understanding canine genetic size facilitates the creation of an individual health plan

Scientific breakthroughs have enabled a better understanding of the genetics underlying dog size. In the future, information on genetic size may facilitate selecting the right individual for different size associated hobbies, or creating a size associated diet and exercise plan for each individual. All MyDogDNA2015 and MyDogDNA2016 tested dogs will automatically have the new size markers reported in their MyDogDNA profiles. All customers with these products now have the opportunity to learn more about the size associated alleles present in their breed, and have their dog’s weight and height visualized in a size chart. In this way, a dog’s size associated markers can be compared with other dogs within the same breed. Breed-defining chondrodysplasia is reported to all MyDogDNA2016 tested dogs.

The scientific basis

The new marker findings are based on previously published research articles: Rimbault et al 2013; Derived variants at six genes explain nearly half of size reduction in dog breeds and Parker et al 2009; An Expressed Fgf4 Retrogene is Associated with Breed-Defining Chondrodysplasia in Domestic Dogs. By using statistical methods, our research team has recently studied the aforementioned size associated markers, and evaluated the effects of short-leggedness on dog height in almost 17 000 dogs and in over 100 ancestral canidaes. According to our comprehensive and independent study sample, all of the studied genetic markers were confirmed to have a size reducing effect on dog size, as reported in the original publications. According to our study, the allele combination carried by an individual predicts its size range well, whereas the allele frequencies predict the size range of the breed. The fixed alleles in the breed (only one allele of the specific size marker is found in all breed members) predict the size range of the breed better than the allele combinations.

Our research team studied also the effects of the breed-defining chondrodysplasia on the dog height. The effect was evaluated, and many new breeds, such as Norfolk Terrier, Australian Terrier, Cesky Terrier and Sealyham Terrier, were observed to include genetically short legged individuals. Breeds with breed-defining hondrodysplasia, based on previous studies, were again confirmed as genetically short legged breeds. 

The ancestral and derived alleles

The ancestral allele (i.e. the ancestral gene form generally present in wild canids) of the studied size markers is associated with larger canine size whereas the derived allele (i.e. altered form of the gene compared to the ancestral alleles) is mostly encountered in smaller breeds. In general, the more derived alleles present, the smaller the dog. The most prevalent marker combination has only ancestral alleles in it. The weight distribution within this group varies from the primitive Cirneco dell‘Etna with the average weight of 10 kg (22 lbs.) up to another ancient breed, the Tibetan Mastiff, with the average weight of 83 kg (183 lbs.). Some breeds appear to be fixed only to the ancestral combination. These breeds are Pyrenian Mastiff (76 cm, 62 kg / 30“, 137 lbs.), Beauceron (66 cm, 34 kg / 26”, 75 lbs.) and Akita Inu (64 cm, 40 kg / 25” 88 lbs.). In addition to the breeds that carry only the ancestral combination, also the Norwegian Lundehund, due to its genetic isolation, has only one size marker combination in all breed members. However, the same combination as in the Norwegian Lundehund is also encountered in dogs from about 30 other breeds that have an average weight from 2.5 kg to 12.5 kg (5.5 lbs. to 27.5 lbs.).  

The more ancestral alleles in a combination, the larger the dog – the strong and weak size markers

As a general guideline, the more the dog has ancestral alleles, the larger the dog is; the more there are derived alleles, the smaller the dog size is. The most common derived alleles IGF1, GHR1 and STC2, are found in most breed size categories, and their size reducing effect is moderate. However, the more numerous these alleles are in the combination, the stronger their reducing effect on dog size. The strong derived alleles GHR2, HMGA2 and IGF1R are mostly found in small or medium sized dogs. With the rare allele combinations that contain more derived alleles the size prediction of the dog is more accurate, even with only six markers. Quantitatively, dogs that are 20-32 cm (8 “- 13”) in height carry derived alleles most frequently, and in fact, the only breeds with two derived alleles of all the markers are Affenpinscher (25 cm, 5 kg and / 10“, 11 lbs.), Maltese (25 cm, 3.5 kg / 10”, 8 lbs.) and Chihuahua (1.8 kg and 19 cm / 7”, 4 lbs.). Short-leggedness (breed-defining chondrodysplasia) also affects the dog height in many breeds. In our study, it was discovered that dogs with breed-defining Chondrodysplasia are about 1.4 times shorter in height compared to normal legged dogs with similar weight.

Size scale prediction is possible by using size marker combinations

The genetic variation between and within the breeds allows phenotypic diversity. Therefore, all dogs are individuals in terms of both character and appearance. As all characteristics, also dog size may vary within the breed, and usually many different marker combinations are found within the same breed. Even if it is not yet possible to predict dog size exactly, certain marker combinations are limited to certain size ranges of dogs. Identification of size associated genetic markers may help to understand the genetic variation affecting dog size and dog growth. Dog size is certainly inherited in part, but also the environment has its share in determining what kind of an adult each individual grows up to become.

 

References:​

Rimbault, M.; Beale, H.; Schoenebeck, J.; Hoopes, B.; Allen, J.; Kilroy-Glynn, P.; Wayne, R.; Sutter, N. & Ostrander, E. 2013. Derived variants at six genes explain nearly half of size reduction in dog breeds. Genome research, 1985-1995.

Parker, H.; VonHoldt, B.; Quignon P.; Margulies E.; Shao S.; Mosher, D.; Spady, T.; Elkahloun, A.; Gargill, M.; Jones, P.; Maslen, C.; Acland, G.; Sutter N.; Kuroki, K.; Bustamante, C.; Wayne R.; Ostrander, E. 2009. An Expressed Fgf4 Retrogene is Associated with Breed-Defining Chondrodysplasia in Domestic Dogs. Science 325: 995-998.

Julia Bouirmane; Genetic variation influencing body size in purebred dogs http://www.theseus.fi/bitstream/handle/10024/112499/JuliaBouirmane130327...