Annika Berner M.Sc.
Introduction
Dog breeding is a complex process influenced by various genetic factors.
Phenotypic variation is divided into over 350 distinct breeds globally, each representing a closed population with specific genetic characteristics [^1^].
Understanding genetic diversity, inbreeding, and breeding practices is crucial for responsible breeding and maintaining healthy dog populations.
Genetic Diversity in Dog Breeds
Genetic diversity is essential for the overall health and resilience of dog breeds.
Studies have shown that some pedigree dog breeds exhibit high levels of inbreeding and a significant burden of inherited diseases, not necessarily related to intentional breeding selection [^3^].
Evaluating genetic diversity in dog breeds involves both genealogical and molecular marker studies [^2^] [^4^].
Inbreeding Principles
Inbreeding, the mating of closely related dogs, is a common practice in breeding to establish uniform quality and reliable inheritance. The inbreeding rate is the probability that a randomly chosen pair of genes in an offspring contains two identical alleles from the same ancestor [^2^].
For instance, in half-sister mating, the inbreeding rate is 12.5%, resulting in a decrease in heterozygosity by the same percentage [^1^].
It's essential to note that inbreeding is not inherited. If the parents of a dog are not related, the inbreeding rate of the puppies is zero [^1^].
While inbreeding aims to accentuate desired traits, it also increases the likelihood of harmful recessive alleles appearing in the offspring [^2^].
Adverse Effects of Inbreeding
Maintaining a balance in inbreeding is crucial, as adverse effects start to appear when the inbreeding rate exceeds 10%. This can lead to decreased fertility, increased puppy mortality, deformities, weakened immunity, and susceptibility to inflammation – collectively termed "inbreeding regression" [^2^]. It is recommended to keep the inbreeding rate below 6.25% over 4-5 generations to mitigate these risks [^2^].
Effective Population Size
The effective population size plays a vital role in preventing the degeneration of breeds due to inbreeding.
It is recommended that the effective size should be at least 100 in the short term and much larger in the long term, up to a thousand individuals [^2^].
However, achieving this long-term goal is challenging for most dog breeds, necessitating strategic crossbreeding [^2^].
Maintaining a large effective size involves using dogs of the breed and family lines for breeding as widely as possible. Incorporating strains from abroad can also contribute to introducing new genetic material [^2^].
Hereditary Diversity and Breeding Progress
Hereditary diversity, characterized by the abundance of gene forms (alleles), is crucial for overall vitality and protection against hereditary defects and diseases.
The narrowing of the gene spectrum can lead to inflammatory diseases, autoimmune diseases, and allergies [^2^].
Breeding progress relies on hereditary variation between dogs.
Even in large dog breeds, diversity can be limited if a small part of the breed dogs and family lines are used for breeding.
Dogs with too many offspring can spread harmful mutation alleles throughout the breed [^2^].
In an ideal situation, dogs from all lineages of the breed should be evenly used for breeding.
Recommendations suggest limiting a dog's lifetime number of offspring to ensure diversity, with specific percentages based on the breed's population size [^2^].
Population Structure and Inbreeding
The genetic diversity of a dog population is influenced not only by the selection of breeds but also by individual breeding dog inheritance.
Ensuring that each breeding dog's inheritance in the stock is not unreasonably large helps keep the gene base of the population broad [^2^].
The effective population size is a critical factor in expanding the breeding base effectively. Calculated using the formula They=4Nm, it involves considering the number of breeding males (Nm) and breeding females (Nf) [^2^]. The minimum effective population size should be around 150-200 breeding dogs [^2^].However, the calculation formula for effective population size assumes that each individual has approximately the same number of offspring. In reality, when dogs are closely related, the effective population size is considerably smaller [^2^].
Conclusion
Understanding the principles and practices of genetics in dog breeding is essential for maintaining healthy, diverse, and resilient populations.
Breeders need to balance inbreeding, genetic diversity, and effective population size to ensure the well-being and longevity of their breeds.
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Sources 1
Genetics of Dog Breeding 2
Genetic diversity, inbreeding and breeding practices in dogs: Results from pedigree analysis 3
Trends in genetic diversity for all Kennel Club registered pedigree dog breeds 4
Evaluation of Genetic Diversity in Dog Breeds Using Pedigree and Molecular Analysis: A Review 5
Genetic diversity – managing inbreeding 6
Population Genetics in Practice Principles for the Breeder