Scientific Principles of Dog Breeding
Prof Alan G. Fahey
Associate Professor of Animal Breeding,
School of Agriculture and Food Science, University College Dublin.
The domesticated dogs’ (Canis familiaris) genome is made up of 39 pairs or 78 chromosomes, compared to 23 pairs or 46 chromosomes for humans. Theses 78 chromosomes are made up of 76 autosomes and are non-sex chromosomes and two sex chromosomes, the X and Y chromosomes. Similar to humans, male dog carries the Y chromosome and have XY sex chromosomes and females carry the X chromosome and have XX sex chromosomes, therefore the male dog determines the sex of the pups. As chromosomes are in pairs, a pup gets one of the pair of chromosomes from its sire and one chromosome from the dam during the formation of the embryo at fertilisation.
Chromosomes are divided into genes which are the basic units of hereditary and carry segments of DNA. The domestic dog has approximately 19,000 genes and these genes form random combinations known as a genotype (Ostrander and Wayne, 2005). The observed measurement of a trait is called a phenotype and the phenotype is a combination of the genotype and the environment and the interaction between the genotype and the environment. In animal breeding terms, the environment is any non-genetic external factor than can affect a dog’s performance e.g. diet, housing and exercise programme. Many of the traits that are of interest to dog breeders such as morphological and health traits are complex traits under polygenic control. This means that these complex traits are influenced by many genes whose expression can be influenced through the interaction with other genes and these genes may also interact with the environment (Bourdon, 2000).
When developing a scientific dog breeding programme, it is important to know how much the variation of the trait is due to the genetic and environmental components. The variation of a trait that is due to transmittable genetic effects is quantified using a metric called the heritability. The heritability is a population value and can have a value between 0 and 1. The heritability is then used to estimate the Predicted Transmitting Ability (PTA) and the PTA is the genetic value that a sire or a dam can pass on to their offspring. If the PTA is known for important traits, they are a valuable tool for dog breeders when making mating decision to improve the health and welfare of their dogs, as well as traits to do with growth, speed, stamina and other traits that may be important.
Traits such as hip dysplasia and elbow dysplasia have heritability values ranging between 0.01 and 0.69 depending on the dog population (Oberbauer et al., 2017). These values are less than one, which means they are not under complete genetic control, which in effect means that if a young dog develops either of these conditions it may not be the fault of the breeder as the dogs’ environment such as diet and exercise, can also contribute to these conditions.
An understanding and the application of the basic principles of scientific principle of dog breeding can contribute to improving the health and welfare and the overall genetic sustainability of a dog population. It is important to note that the development a scientific breeding programme for dogs will contribute to permanent and cumulative improvement over time.
References:
Bourdon, R.M. 2000. Understanding Animal Breeding. Second Edition.
Oberbauer, A.M., G.G. Keller, and T.R. Famula. 2017. Long-term genetic selection reduced prevalence of hip and elbow dysplasia in 60 dog breeds. PLOS One 12(2): e0172918. Doi:10.1371/journal.pone.0172918.
Ostrander, E.A, and R.K. Wayne. 2005. The canine genome. Genome Research 15:1706-1716.
Glossary of Terms
Chromosome:- a long strand of DNA and proteins located in the nucleus of every cell.
Environment: - non-genetic factors that can influence an animal’s performance.
Gene:- basic hereditary unit containing a DNA sequence.
Genotype:- the genetic make-up of an individual
Heritability:- a measure of the relationship between the performance of a dog for a trait and its genetic value.
Phenotype:- the level of performance of trait for a dog.
Polygenic:- a trait affected by many genes.
Predicted transmitting ability: half of the genetic value of animal. It is the part that is transmitted to the offspring.