The Independent Inquiry into Dog Breeding



The Independent Inquiry into Dog Breeding by Patrick Bateson:

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Inquiry Files

This quote sums up what Anglo Wulfdog breeders are doing:

"The larger breeders can play very important roles in breeding away from poor health conditions that have become established in a breed. When enough genetic variation exists in a breed, it is possible to select individuals for mating that do not carry the defect. If not, outcrossing to a different breed should not be regarded as an abomination.   Outcrossing can sometimes carry health risks, but several cases have established that once the out-crossed puppies are obtained, artificial selection can ensure that healthy dogs with the desired features of the breed are rapidly recovered."


This is an extract from the report, for those of you who don't have time to read the whole thing.   It backs up what the Anglo Wulfdog breeders have been saying for a very long time.

Chapter 3, Genetics and Inbreeding

The genetics of inbreeding is reviewed. Animals that are inbred are less likely than optimally outbred animals to survive and less likely to reproduce. Inbreeding can result in reduced fertility both in litter size and sperm viability, developmental disruption, lower birth rate, higher infant mortality, shorter life span, reduction of immune system function, and increased frequency of genetic disorders.

3.1 Any thoughtful breeder of dogs should be concerned about the potentially adverse effects of inbreeding, but breeders are typically faced with a dilemma. Their impulse is typically to go for purity in order to fix desirable qualities and, if that means mating two dogs that are closely related, desire for purity often wins over any fears about inbreeding too much. The conflict between preserving desirable characteristics and avoiding the potentially unfavourable outcomes that may accompany inbreeding is real. Before exploring this dilemma any further, it is worth clearing up some common confusions.

3.2 Some breeders will tell you that they are not inbreeding, they are ‘line breeding’. What is meant by this is that the breeder is carefully selecting mates on the basis of a detailed knowledge of their genealogy and their family’s breeding history. Sometimes this is done to avoid perpetuating a recognisable inherited disease. More usually they are choosing mates carefully to generate, it is hoped, prize-winning characteristics. I shall have more to say about both these actions by breeders in Chapter 6, but either way, if the breeder mates, say, grandfather with granddaughter, he or she is inbreeding and doing so to a marked extent.

3.3 If inbreeding versus line breeding is a distinction without a difference, another confusion arises where two different ideas have been run together, namely inbreeding and incest. Incest is a culturally-transmitted prohibition which, in my view, should be applied exclusively to humans. The reluctance to mate with a close relative is an inhibition found in many other animals apart from humans (Bateson, 2004). Incest taboos may have arisen indirectly from inbreeding inhibitions, but the taboo is often applied to individuals who are not genetically related. The back of the Church of England’s Book of Common Prayer states, among other restrictions, that a man may not marry his wife's father's mother or his daughter's son's wife. The mind boggles at the possibility, but clearly no genetic relationship is entailed here.

3.4 Unquestionably inbreeding can lead to a loss of biological fitness. The animals in the inbred lineage are less likely to survive and less likely to reproduce than animals in more outbred lineages. This has been demonstrated many times in well-studied, naturally outbreeding species. Inbreeding can result in reduced fertility both in litter size and sperm viability, developmental disruption, lower birth rate, higher infant mortality, shorter life span, increased expression of inherited disorders and reduction of immune system function. The immune system is closely linked to the removal of cancer cells from a healthy body (Smyth et al., 2006), so reduction of immune system function increases the risk of full-blown tumours. Many of the effects of inbreeding have been found in isolated populations of wolves, the wild ancestors of domestic dogs, with detrimental effects (Laikre & Ryman, 1991). Severe inbreeding depression has been documented in Scandinavian wolves that had passed through an extreme bottleneck (Liberg et al., 2005). During their first winter after birth the number of surviving pups per litter was strongly and inversely correlated with how inbred were the pups. The more inbred they were, the less likely were they to survive. Given what happens in wolves, domestic dogs should be no exception to the rule that breeders should avoid close inbreeding as much as possible.

3.5 Most genes of sexually reproducing species come in pairs. Each member of the pair is referred to as an allele by geneticists. Most genetic mutations, if they have any effect at all, tend to reduce or sometimes even remove a gene's function. Having genes in pairs is therefore a good thing because one good copy is usually enough, problems only arising when the members of a pair are the same (or homozygous) and both an individual's copies are defective or, in rarer cases, where the defective gene is dominant. Defective gene copies that only reduce health when a good copy is absent are called 'deleterious recessives' and are generallyrare, making it extremely unlikely that their effects are felt. However, when two closely related individuals mate, the resulting offspring can inherit the same gene copy from a single recent ancestor. If that copy is a deleterious recessive, the offspring may be unhealthy. In this way inbreeding can expose latent genetic problems by increasing the chance that an individual carries two identical, defective copies of a gene. (Inbreeding also has other effects that are described below.) When animal breeders wish to produce pure genetic lines, as they sometimes do, for example in laboratory animals, they will mate brother with sister generation after generation. Most lines die out due to the exposure of deleterious recessives that are normally hidden. However, any healthy lines that survive are likely to have lost many of the deleterious recessive genes they started with, a process known as genetic purging. Purging can occur in natural populations that are reduced to very low numbers forcing them to inbreed, and may account for why sea mammals, that went to the brink of extinction, have recovered remarkably well (Clapham et al., 1999).

3.6 Conservation is a high priority for Zoo Directors and Curators concerned with protecting rare species. Rarity may arise because the world population is small or because importing that species from the wild is illegal. Either way, this means that zoo personnel and, for that matter, wildlife managers need to keep a sharp eye on inbreeding and to be well informed about conservation genetics. Many good text-books have been written on the subject (e.g. Frankham et al., 2002). 

3.7 Massive improvements in molecular techniques have meant that it has become easier to characterise the effects of inbreeding (Lindblad-Toh et al., 2005). When one gene is responsible for a genetic defect that gene can be identified. I shall return to the implications of these advances in Chapter 6, but a word of warning is required here. If genes interact with each other or with the environmental conditions in which the animal is kept, then the benefits of DNA analysis to the breeder will be much less.

3.8 Heritability is a concept used by geneticists and can be thought of as the extent to which, for any given character, offspring resemble their parents. Heritability is important in selective breeding programs because traits with low heritability are much less responsive to selection. In population genetics high heritability means that the additive variation due to the genes is high. In this narrow sense, the measure is indicative of the extent to which the variation in the population is due to variation in genes considered independently of their interactions with other genes at the same or at different loci. More broadly, heritability refers to the ratio of the spectrum of differences in a characteristic due to genetic variation to the total spectrum of the phenotypic trait in the population. A trait has high broad sense heritability in a population to the extent that the existing variation for that trait in the population is due to genetic variation. None of these definitions refers to the characteristics of an individual since they all relate to traits found in populations of individuals.

3.9 If statistical variance in a trait is entirely due to variability in the genes, broad sense heritability is 1.0; if it is entirely due to the influence of the environment, broad sense heritability is 0.0. Behind the deceptively plausible ratios lurk some fundamental problems. For a start, the heritability of any given characteristic is not a fixed and absolute quantity. Its value depends on a number of factors, such as the particular population of individuals that has been sampled. For instance, if weights were measured only among well-fed dogs, then the total variation in weight would be much smaller than if the sample also included dogs that were small because they had been undernourished. The heritability of weight will consequently be larger in a population of exclusively well-nourished dogs than it would be among dogs drawn from a wider range of environments. Thus, the heritability of weight is likely to be lower in, say, purebred Labradors, where most of the genes influencing weight are similar, compared with a more heterogeneous population where, say, Labradors and Fox Terriers are allowed to interbreed.

3.10 The most serious weakness with heritability estimates is that they rest on the assumption that genetic and environmental influences are independent of one another and do not interact. The calculation of heritability assumes that the genetic and environmental contributions can simply be added together to obtain the total variation. In many cases this assumption is clearly wrong and an overall estimate of heritability has no meaning, because the effects of the genes and the environment do not simply add together to produce the combined result. This has important implications for the advice that should be given to breeders.

3.11 Estimated breeding values (EBVs) describe the relative genetic value of each member in a breeding population. They can also be used as a basis for choosing which animals are the best candidates to select for breeding to produce the next generation of offspring. Livestock and plant breeders have used estimated breeding value techniques for years to obtain genetic improvement in their breeding lines. The values are usually applied to a single characteristic of the animal or plant and are derived from heritability estimates. Therefore, they are subject to some of the concerns that I have raised in the previous paragraphs. However, they may be of some help to the breeder in choosing a suitable mate particularly when attempts are being made to eradicate a serious inherited disease.

3.12 A desirable characteristic that is highly amenable to artificial selection can lie close (on a chromosome) to another gene that has much less desirable characteristics. The process of selection can, therefore, have entirely unintended consequences due to what is known as linkage. This may be rare but its possibility has implications to which the breeder should be sensitive when attempting to shape the characteristics of a line of dogs.

3.13 Professional geneticists have produced simple rules for calculating what would be likely to happen if two related individuals were mated. The chances that two half siblings, having only one parent in common, will inherit the exact same copy of any given gene from their common parent is a quarter. This is because, when parents create sperm or eggs for reproduction they halve the number of genes, with only one gene in each pair being present in the gamete. The halving process is assumed to be random so that when the relationship to the half-sibling is calculated, the metaphorical coin has been tossed twice as it were, and the link between the two individuals is obtained through the path from one to the common parent and back to the other. (Technically this is expressed as 1/2n where n is the number of steps in the path or paths linking two individuals.)

3.14 When the same method is applied to full siblings, the links are through both parents so the chances of their sharing the same rare gene is a quarter plus a quarter, namely a half. This number is called the coefficient of relationship. When, as commonly is the case in dog breeding, the same sire is used many times, a dog may be the grandfather and even the great-grandfather of its potential mate. The same counting method can be used as before. The number of steps from the female to her grandfather is two and the number of steps to her great-grandfather is three. So the coefficient of relationship is 1/22+1/23 which equals 0.375. Obviously, if manifold links exist in the pedigrees of the two dogs, the coefficient of relationship between two individuals will be higher than simply looking at the closest relations of the potential mates.

3.15 A further consequence of using the same sire for  many matings is that the level of inbreeding is greatly increased. The phrase that is commonly used is effective population size, which means the population is equivalent in size to an idealized population in which a level of inbreeding is the same as that actually observed. Calboli et al. (2008) have calculated the effective population size for ten breeds of dog, exploiting one of the world's most extensive resources for canine population-genetics studies: the UK Kennel Club registration database. They analysed the pedigrees up to around eight generations before the present and found extremely inbred dogs in each breed except the greyhound. They estimated an effective population size between 40 and 80 for all but two breeds. These low numbers were obtained in breeds where the actual population sizes were often in the thousands.

3.16 The random way in which genes are reduced from pairs to singletons in the formation of sperm or eggs has a consequence that is particularly important in inbred populations. Purely by chance certain genes may be lost. This occurs much more quickly in small populations. The process is known as genetic drift. Once genes have been eliminated they cannot be recovered except by outcrossing or by very rare mutations.

This means that, when the effective population size has been drastically reduced (bottlenecked) by selective breeding or, under natural conditions, by an environmental catastrophe, regrowth of the population will be strongly affected by what are known as founder effects. The genetic structure will inevitably be constrained by what was left at the time of the bottleneck.

3.17 Despite severe bottlenecks, small populations can survive. A famous case is provided by the white Chillingham cattle kept in a Northumberland park. The claim is that these cattle have been kept in an isolated state for seven centuries. Whether or not that is correct, the herd was reduced to 13 in the severe winter of 1946-47. Since then it has re-grown to more than 80 animals. Another famous example is Przewalski’s horse which became extinct in the wild but was then re-grown from nine individuals to more than 1500, admittedly after some crossing with domesticated horses, and has been successfully reintroduced into the wild. Zoos are continuously faced with breeding from tiny numbers and whole populations may have a single pair of individuals as common ancestors.

3.18 Purging of alleles with seriously damaging effects can carry obvious benefits. In the process of inbreeding, other alleles with less serious effects can become homozygous and can be retained in the  population. Outcrossing to introduce fresh blood can mitigate such effects by introducing greater variability into the gene pool, but outcrossing does carry the danger that the benefits of purging are undone by introducing new deleterious recessives.

3.19 While inbreeding is generally seen as being undesirable, the debate has become much more nuanced in recent years. By no means all inherited diseases are carried by single pairs of genes. Many inherited diseases arise from the interaction of the products of several genes. If one or more of these genes contributing to the inherited disease are eliminated by genetic drift or by skilful breeding, then the disease may no longer be seen in the offspring.

3.20 Excessive outbreeding can also carry costs and in  many species adaptations to local conditions or complexes of genes that work well together can be broken up by outcrossing. I discussed the issue of optimal out-breeding more than a quarter century ago (Bateson, 1983) and a growing body of data from fish (Kalbe et al., 2009) to humans (Helgason et al., 2008) supports that view. Whether or not this is true for any breed of dog has yet to be established. In many human cultures first cousin marriages are commonplace. Relationship in such a marriage is 0.125 and the ill-effects are generally small, although much debated (Bittles, 2008).

However, when repeated generation after generation, previously unsuspected ill-effects of inbreeding can emerge. Compared with a first cousin mating, the genetic risk associated with a grandfather-granddaughter mating, often used in pedigree dogs, is doubled, and where cumulative inbreeding has occurred (paragraph 3.14) the genetic risks increase proportionately.





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