Breeding Against Anomalies
The existing breed variety of dogs presents a unique opportunity to study the genetic control of numerous morphological characters, a different combination of which determines breed standards. Two of the existing breeds of a domestic dog can serve as an illustration of this position, contrasting with each other at least in such morphological characters as height and weight. This is a breed of English mastiff, on the one hand, whose representatives have a height at the withers of 80 cm and a body weight of more than 100 kg, and a breed of chi hua hua, zo cm and 2.5 kg.
The process of domestication involves the selection of animals according to their most prominent features, from a human point of view. Over time, when the dog began to be kept as a companion and for its aesthetic appearance, the direction of selection changed to producing breeds that were poorly adapted to survive in nature, but well adapted to the human environment. It is believed that “mongrels” are healthier than purebred dogs. Indeed, hereditary diseases are more likely to occur in domestic animals than in wild ones.
Outbreeding can mask the effect of many recessive genes. Human intervention in selection and inbreeding promotes homozygosity, and thus recessive genes appear, but the identification of these genes makes it possible to eliminate them by further selection. The main goal of breeding work is to maximize genetic progress in animal populations. Such a formulation of the question requires the creation of an integrated multifunctional system, which includes both optimization of selection methods and the creation of optimal paratypical conditions conducive to the maximum manifestation of the genetic potential of animals.
“One of the most important goals is the development of methods for combining the tasks of improving animals according to breeding traits and maintaining their fitness at the necessary level, as opposed to the unilateral selection of the maximum (sometimes exaggerated, excessive) development of specific breed traits, dangerous for the biological well-being of domesticated organisms” - (Lerner, 1958).
The system of pedigree work in dog breeding that has developed in our country, as a rule, is confined to the framework of not even individual clubs, but separate nurseries. This is clearly seen in the example of breeding defects, in the occurrence of which experts play a significant role. The same applies to the so-called "specialists", who often talk about some defects, often minor ones, and are not able to see the main thing.
The efficiency of selection, we think, should consist in diagnosing anomalies in affected animals and identifying carriers that have a defective heredity, but with a normal phenotype. The treatment of affected animals in order to correct their phenotypes can be considered not only an event to improve the aesthetic appearance of animals (oligodontia), but also the prevention of cancer (cryptorchidism), the preservation of biological, full-fledged activity (hip dysplasia) and the stabilization of health in general. In this regard, selection is necessary against anomalies in the joint activity of cynology and veterinary medicine.
An important stage of breeding work is also the selection of characters by which the selection should be carried out, and their comprehensive comprehensive assessment. The most suitable method in this situation is "systems approach". It requires the breeder to have detailed knowledge of the significance of each trait and how much its value depends on environmental influences, as well as the need to apply modern achievements in the field of population genetics and reproduction biology. Since zootechnical scientists are engaged in agricultural species of animals that serve as a source of food and raw materials, publications on scientific selection and breeding in dog breeding are extremely rare.
The ability to test DNA for a variety of dog diseases is a very new thing in cynology; knowing this can warn breeders about what genetic diseases they should pay special attention to when selecting breeding pairs. Good genetic health is important because it determines the biologically full life of the dog.
Dr. Pagett’s book, “Dog Genetic Disease Control,” shows how to read a genetic lineage for an anomaly. Genetic genealogies will show whether this disease is sex-related, or inheritance goes through a simple dominant gene, or through a recessive, or polygenic disease by origin. Unintentional genetic errors will occur from time to time regardless of the thoroughness of the breeder's work. Using genetic pedigrees as a tool in the exchange of knowledge, one can dilute the “harmful” genes to such an extent that they stop their development until the DNA marker is found to test their transmission.
Since the selection process involves improving the population in the next generation, it is not the phenotypic characteristics of the immediate elements of the selection strategy (individuals or pairs of crossed individuals) that are taken into account, but the phenotypic characteristics of their descendants. It is in connection with this circumstance that the need arises to describe the inheritance of a trait for breeding problems. A pair of interbreeding individuals differ from the rest of the same individuals in their origin and phenotypic characteristics of the trait both themselves and their relatives. Based on these data, if there is a ready-made description of inheritance, one can obtain the expected characteristics of the offspring and, therefore, assess the breeding values of each of the elements of the breeding strategy.
For any measures directed against any genetic anomaly, the first thing to do is determine the relative importance of the “bad” sign in comparison with other signs. If an undesirable trait has a high heritability rate and causes serious harm to the dog, proceed differently than in the case of a rare manifestation of the trait or its secondary significance. A magnificent breed-type dog, transmitting a vicious color, remains a much more valuable producer than a mediocre, but with the right color.
The problems of cryptorchidism, dysplasia, hermaphroditism, difficult labor, behavior that does not correspond to the breed type remain relevant. To identify carriers, you must be able to correctly compose a program. The above anomalies are interconnected since this is a manifestation of systemic effects, indicating that the genome is losing its stability. This heterogeneous mass of violations is a fan of reactions of an unstable genome, a reflection of serious changes in the biochemical status of the organism. The most significant obstacle in this case is the unsystematic introduction of new foreign genomes into the existing population, that is, increased interpopulation hybridization and, accordingly, hybrid dysgenesis. Before using foreign manufacturers widely, it is advisable to test them for the quality of offspring on a limited number of mating. The appearance of a large number of systemic abnormalities in the offspring will be an indicator of dysgenesis.
When selecting manufacturers, the main criterion is the titles obtained at exhibitions by the manufacturers themselves. Fewer breeders are resorting to specialist assistance in pairing, using their empirical methods. It seems logical that the main breeding units that make the maximum contribution to the livestock are male dogs, usually “imported” and not always of the desired quality. Since the influence of an individual male on the general condition of the breed is much stronger than the influence of any individual female (unless she gave birth to several unique sons), the development of the breed is more dependent on the correct selection of males than females.As a result, when selecting: “he has just been brought from abroad” and “he has just received the title of champion”, the rate of genetic progress of populations and the efficiency of breeding are underestimated.
In almost all countries of the world, a three-stage scheme has been adopted for breeding producers, which includes:
selection by own productivity,
selection by reproductive ability,
selection in breeding groups according to the results of an assessment of the quality of offspring.
The main stage of selection, on which the resulting selection effect largely depends, is the assessment of producers by the quality of the offspring.
At the same time, one should not forget about hereditary anomalies, which may not be available for the selected manufacturer, but may be for his brothers and sisters. Aspiring to a more correct head structure in dogs, breeders of any breed may encounter problems, especially with a bite and overshot. It is believed that selection on a massive head will lead to brillost and excessive dampness, and signs of chondrodysplasia affect the massive skeleton more than the lung. It was found that an increase in the skeleton inevitably leads not only to an increase in body size and weight, but also to a change in the exterior as a whole, straightening of the angles of the joints of the hind limbs, congestion of the croup, and sheer set of blades.
Back in 1930, N.A. Ilyin identified elementary signs of the structure of the dog’s skull, among which were considered: the orbital angle — on this basis, there are major differences between the skull of a wolf and a dog. Inheritance of this trait was intermediate in comparison with a small and a large angle in the parent pair. The wide shape of the skull dominated the narrow, just as the wide jaws dominate the narrow. The normal number of teeth dominates their reduced number.
Selection is the only way to eradicate unwanted traits, and carriers should be discarded from the breeding. The basis of breeding for most domestic animals is that unwanted alleles tend to have recessive inheritance. Hidden in the genotype, recessive alleles, becoming homozygous, immediately appear in the phenotype, we observe this phenomenon by inbreeding.
One of the most successful master breeders of our time, Pat Trotter, said about the study of pedigrees: “When you look at an animal’s pedigree, it tells you how it should be, when you look at an animal in the ring it tells you about how it seems. And when you look at his descendants, it tells you what it really is. ”
Dr. Rainer Boeing from the Institute of Animal Husbandry and Pet Genetics, University of Giessen, Justus Liebig (Germany), proposed a method for identifying not only affected animals, but also those with dysplasia, based on the use of a selection index.
An analysis conducted using electronic databases on German thoroughbred dogs allowed Rainer Boying to calculate indices that describe how the genes of the dog being evaluated will have a specific trait in its descendants. Indexes are usually denoted by the abbreviation ZW (from the German Zuchtwert - breeding index). Their calculation is based on electronic databases containing information about dogs of a particular breed.
Since 1988, Germany has been calculating selection indices for a variety of characteristics and for different breeds. According to some sources, the calculation of ZW for dysplasia in Germany is carried out in 50 breeds. Such calculations were performed by Dr. Boeing, using the example of German Shepherds. He compiled a system of 485914 equations, taking into account including 236 billion family ties between dogs, neglecting the conditions of breeding. As a result of the calculation, the average level for the breed was determined, which received a relative weight of 100. This is the selection index (ZW). In animals with the best indicators, the ZW values turned out to be less than 100, with the worst - more than 100. In general, the scatter was from 70 to 130 (min 65 - max 180). The majority of dysplasia-free dogs had a ZW of about 85.
Various defects are an inevitable problem of any biological species, not excluding humans. In the case of a dog, at least you can evaluate and study some of these defects, as well as take measures to deal with them. They cannot be ignored, it cannot be argued that defects need not be worried - this is an obvious misconception. However, do not go to the other extreme, a painful fear of defects, as if fleeing from defects and anomalies was the main goal of dog breeding.
Many characteristic morphological characters of a mutational nature and fixed in various dog breeds as leading exterior characters can unexpectedly sporadically occur in dogs of other breeds. Widely known are a number of such mutant forms, which are most often inaccessible for genetic analysis due to culling of dogs with observed deviations from the norm. The anomaly of shortening of the upper jaw - “bulldozhism” became a breed sign for boxers, bulldogs, khins, etc. In many cases, when this symptom occurs, it is associated with a wide pleiotropic effect, this can be expressed in splitting of the nose, the appearance of a cleft lip and a wolf’s mouth, ”in violation of the dental and respiratory systems, which often leads to death.
For cynology, first of all, the health problem of not every such anomalous individual is relevant - but the health problem of the entire population, breed. And in this regard, it seems absolutely necessary selection against anomalies. At the same time, the interests of veterinary medicine and cynology form a common "field" in the diagnosis of anomalies. Without this, effective selection is impossible, which, according to S.P. Knyazev and colleagues at Novosibirsk University, should be carried out according to the following algorithm:
Analysis of anomalies: creating a database, elucidating genetic conditionality, establishing the type of inheritance.
Development of a strategy for working with the breed: assessment of the "genetic load", determination of the "specific gravity" of the anomaly in the complex of breeding traits, development of target parameters.
Selection: establishing acceptable selection boundaries - by phenotype in the population, by genotype - in the tribal core.
Selection of producer pairs according to their genotypes.
Correction of phenotypes of offspring in the process of growing it.
Once again, selection is in the next generation.
It should also be emphasized that the exterior of most, if not all breeds, is in continuous connection with the behavior inherent in this breed. Therefore, breeding only on the exterior without taking into account behavioral characteristics is unpromising and dangerous. One of the first serious studies of dog behavior should be considered the work of I.P. Pavlov on conditioned-reflex activity, as well as the works of L.V. Krushinsky, D.K. Belyaev. Due to the great complexity of behavioral reactions, the study of their inheritance usually comes down to assessing the heritability coefficients, various correlations of morphological and behavioral traits, and much less often, to direct genetic control.
The evolution of behaviors has undergone numerous changes, in connection with this, the analysis of a variety of morphological and behavioral traits in hybrids of dogs and wolves shows that they are prolific and resemble wolves in their behavior.They are characterized by isolation, caution, inability to bark and attachment to one person. There are cases when abandoned dogs were united in packs, such animals in their behavior combine the signs of wolves and domestic dogs that they have preserved at the same time. The use of modern methods, such as, for example, allozyme divergent analysis, mitochondrial genomic analysis, showed that the domestic dog and the gray wolf are much more closely related to each other than to any other representative of the Canidae family, and the degree of their relationship is much higher compared with other studied species from this family.
The main domestication signs are a change in defensive behavior, a change in body proportions, the shape of the ears and tail, and the structure of the coat. According to D.K. Belyaev, the behavior of animals also changes in the process of domestication due to a sharp increase in the level of adrenocorticotropic hormone in the blood, which contributes to the activation of "sleeping" genes, due to which genome destabilization and an explosion of variability arise.
The selection of wild animals is carried out by nature itself, diseases destroy less viable, and predators - weaker. The breeder, even having a very large kennel, does not select according to the laws of natural selection, so he has the opportunity to save those dogs that in nature would be doomed to certain death. Phenotypically extreme variants in conditions of natural selection are eliminated by wildlife. Restrictions on the freedom of interbreeding and inbreeding in human-bred populations create the basis for gene drift, which quickly brings mutations to the surface that were previously hidden under the cover of a wild phenotype.
What is selection?
We will not beat around the bush, but immediately give a definition of selection. So, selection is the selection of dogs within the breed to get the best in terms of the exterior, productivity and nature of the queens.
In order for the selection of dogs to be successful, you need to know its basics. This is heredity, heritability and inheritance.
Natural and artificial selections
In breeding dog breeds, there are two types of selections by which it is conducted. As you can see from the title, they are called natural and artificial. The first is not carried out in modern breeding, because it implies the natural death of unsuccessful pedigree specimens without human intervention.
We will talk about artificial selection in dog breeding in more detail.
The essence of artificial selection
What determines the effectiveness of artificial selection? There are a lot of factors here: starting from environmental conditions, ending with the number of alleles responsible for the formation of a particular trait.
Dog breeding features are based on the genetic nature of artificial selection. Animals are selected according to the following characteristics:
- Against the dominant gene.
- On the dominant gene.
- Against a recessive gene.
- According to the recessive gene.
- In favor of heterozygotes.
- Against heterozygotes.
We know that there are genes that take over all the rest. And if you want to get animals with a certain color, then the selection during the selection of dogs is carried out on the dominant gene. It is necessary to have alleles that are responsible for a particular coat color in both manufacturers. For this, they conduct the mating of the main producers with the subsequent analysis of the work of genetics on the resulting offspring.
Selection against abnormalities in the exterior of dogs
One of the most important tasks of dog breeding, as well as of all modern livestock breeding, is to strengthen the constitution of animals in the process of improving the breeds. The strength of the constitution, as a reflection and guarantee of health and adaptive ability, is, together with pronounced pedigree features, the basis for the desired performance of dogs.
These parameters, which are formed in the process of ontogenesis (development of the organism) during the interaction of heredity and environmental conditions, are absolutely necessary to consider in breeding. This is all the more important because dog breeders have to note cases of birth from apparently normal producers of the so-called abnormal offspring - animals with violations of the structure and functioning of organs and systems of the body. With insufficient attention to the selection (culling) of such animals, the frequency of deviations from normal development sometimes increases sharply, which significantly complicates the improvement of the breed.
Anomalies can be of a different nature, depending on whether they are inherited or not. Genetic (hereditary) is considered those of them that are determined by heredity, genotype. Such abnormalities appear and spread in the rocks as a result of the use of producers of carriers of harmful genes. Most often this is facilitated by the use of closely related mating, inbreeding.
The successes of modern genetics determine the development of private animal genetics, including dog genetics, and the development of scientific selection. Knowing the laws of genetics allows livestock breeders to successfully improve breeds and eliminate hereditary anomalies.
It is possible to establish whether one or another anomaly is hereditary if abnormal puppies are found in litters from producers of related origin or in different litters of the same manufacturer or producer. However, this in itself is not yet complete proof of the genetic nature of the anomaly: after all, a group of related animals is usually kept and bred under similar conditions, is exposed to the same environmental impact, which can cause the manifestation of two types of anomalies.
1. Inherited environmental. Their manifestation depends both on the genotype and on the action of the external environment.
2. Exogenous, arising under the influence of special external factors - teratogens.
Teratogens are of a chemical, physical, biological nature (ultraviolet radiation, some chemicals, pathogens, etc.). It is known, for example, that in bitches who had been ill with parvovirus enteritis during puppies, puppies with various deformities were born repeatedly. In this regard, the requirements for the proper breeding and keeping of animals to obtain full-fledged healthy offspring remain relevant.
Particular attention should be paid to the breeder genetic abnormalities, for which it is possible to establish a specific type of inheritance. This makes it possible to take measures to eliminate or at least at least reduce the frequency of congenital malformations.
Each anomaly separately occurs relatively infrequently, but the total effect of the "hereditary burden" of all congenital deformities can be very noticeable in the breed. Its degree depends on many reasons, including the completeness of the study of the issue. For example, R. Robinson (1982) notes that individual anomalies can sometimes become a scourge for a breed, as happened with the so-called collie eye disease, in those dog associations, where selection and examination to identify this disease is not established, it affects more 80 percent of all Scottish shepherd dogs (collie).
In addition, as shown clearly in a new textbook on veterinary genetics by V.L. Petukhov et al. (1985), the frequency of anomalies encountered depends on the accuracy of birth registration of abnormal animals. There are two aspects. The first is that many abnormal animals are not easy or even impossible to determine at an early age without special diagnostic tests. The basis of the second, especially characteristic of dog breeding, is the breeding stock owned by amateurs. And breeders are often inclined to hide the case of the birth of puppies with deformities to maintain the reputation of the plant. Apparently, all these reasons explain the relatively high frequency and even the recent increase in the prevalence of dog anomalies such as hip dysplasia, umbilical and inguinal hernia, various types of edentulousness, cryptorchidism, and some others.
The frequency of hereditary anomalies usually varies in different breeds and lines, which, by the way, is one of the confirmations of the genetic nature of such deviations, as E.K. Merkuryeva (1986) notes, while hereditary anomalies should be considered an “important characteristic on the basis of which about the state of the population (breed>, its progress and deficiencies. "
The famous American geneticist F. Hutt (1979) published a list of dog breeds in which anomalies known at that time were found with different frequencies. Such a list allows with a certain probability to assume the presence of a specific anomaly in a given breed of dog. Discovered and identified, it can be eliminated with planned breeding, and for this it does not at all need to be transferred to the whole breed. A similar list of all known dog anomalies, classified according to organ systems, indicating the breeds in which they were found, (cited by the famous Swedish specialist A. Hedhammar (1986), The message was published in the collection of works of the Symposium on hereditary diseases of dogs, organized by Kennel Club and the University Agricultural Sciences of Sweden in 1984.
It is important to emphasize that the fundamental approach to eliminating hereditary anomalies of dogs is the use of genetic selection methods, and not therapeutic and prophylactic ones. Progress here is achieved by working with the breed as a whole, at the population level, and not by treating dogs with manifestations of abnormalities, which in some cases can only reduce the severity of the pathology, but not affect the genotype and therefore do not interfere with the infection of the breed in several generations.
Genetic abnormalities arise, as a rule, as a result of mutations - changes in genes. Mutations are random phenomena and can occur unexpectedly at any time in dogs of any breed and in mongrel, and then spread among descendants. By themselves, they can be harmless - such are many changes in color genes that have formed a series of multiple alleles of pigmentation of the coat. However, often mutations violate the existing balance of physiological functions of the body: at one stage of its development, the normal course of biochemical processes is disrupted. A subsequent chain of changes can lead to an anomaly.
The type of inheritance is determined by anomalies by genealogical analysis - studying pedigrees, and genetic - by studying special crosses (mating).
Mutant genes are dominant and recessive. Anomalies are most characterized by an autosomal recessive type of inheritance when the recessive gene is located in the autosome. The presence of such genes manifests itself identically in males and females and only in a homozygous state: the genes combine in one individual, transmitted to it from both parents. In heterozygotes, the action of recessive genes is blocked by homologous dominant alleles. Therefore, abnormal descendants (homozygous recessive) can be born from mating normal phenotypically parents who are genotypically heterozygous. Such anomalies manifest themselves through the generation: it is hidden in the parents, since the mutant gene is masked by the dominant normal gene, and only when two recessive genes are combined in one genotype does an abnormal puppy be born. This is most likely when breeding relatively closely related dogs. It is in this increase in probability that one of the main explanations for the infamous inbred depression breeders lies: it is a consequence of the accumulation in the genotype of many recessive genes in the homozygous state - including genes of various congenital diseases and deformities, most of these genes are recessive and appear in homozygotes, born as a result of closely related breeding.
But is inbreeding itself a cause of anomalies, and they are its inevitable consequences? This question should be answered in the negative. Indeed, the essence of inbreeding (and its value as the most important zootechnical method) is the combination of the ancestor genes received from both parents in one genotype and their translation into a homozygous state. Such a biological property of related breeding — the accumulation and consolidation of the ancestral heredity — is capable of ensuring the creation of animals that persistently transmit their qualities to their descendants due to homozygosity. It can in different cases, depending on the specific breeding situation, either be a powerful factor in improving the breed, or pose a danger to it, threatening inbred depression. Indeed, along with the transfer of the desired genes into homozygosity, there is a danger of a similar process with genes of anomalies and other undesirable traits.
Thus, there is a dialectical interconnection of the breeder’s desire to repeat an outstanding producer by inbreeding descendants and the danger of degeneration. The solution to the problem lies in the specific work, in the selection of methods for selecting and selecting producers by genotype by checking them for the quality of offspring.
Anomalies caused by dominant genes are manifested not only in homozygotes, but also in a heterozygous state. Therefore, if the pathology greatly reduces the viability or affects the working qualities (or exterior) of the animal, it will be eliminated very soon by selection. But exceptions are possible. The English geneticist R. Robinson (1982) in the book "Genetics for Dog Breeders" gives an example with the dominant M gene of marble color. This gene in a homozygous state (MM) also causes the birth of white deaf puppies with visual anomalies. Heterozygotes (Mm - normal marble dogs, well-known and popular among lovers of a number of breeds (Scottish shepherd dogs (collies), mastiffs, dachshunds, hounds, etc.). Knowledge of genetics allows you to get marble puppies, avoiding the birth of unwanted abnormal MM homozygotes. For this marble producers (they, if healthy, are probably Mm heterozygotes) select partners of a different color (their genotype mm) .This selection strategy completely eliminates the risk of MM homozygotes burdened by the inheritance burden diseases.
The dominant gene of anomaly can be preserved in a population in adjacent generations, in such cases when the clinical or exterior manifestations of the pathology are unrecognized before the start of breeding of sick animals, and they transfer their genes to children before they can determine the anomaly of the manufacturer. Therefore, it is desirable to identify such anomalies in the early stages using modern veterinary and biological methods to adjust breeding plans.
Sometimes dominant genes are not manifested in all dogs that have them; the so-called incomplete penetrance of genes is observed. Such carriers of dominant mutations are outwardly normal, although they transmit “bad” genes to descendants, some of which may appear. In these cases, the study of pedigrees gives the impression of illegitimate inheritance, which is why the elimination of such anomalies is usually difficult.
However, most monogenic (determined by one gene) anomalies are still inherited in a recessive manner. Some of the mutant genes - the so-called flying - cause the death of homozygous individuals.
In many animal species, prenatal flies were known, which, even before the birth of the offspring, performed their “role” - the death of embryos. F. Hutt in "Animal Genetics" cites as an example the prenatal fly-bobbling in famous cats from the Isle of Man.Cudtail in them is due to the dominant gene, which is indicated by the letter M (not to be confused with the designation of the gene of marble color). In the homozygous state, the M gene pleiotropically causes the death of embryos, and the born tailless kittens are always heterozygous. When they cross each other, offspring is born in a ratio of 2 tailless: 1 tailed (and not 3: 1, as would be expected if there was no lethality in one class of offspring). In this offspring, there is no class of homozygous MM tailless kittens that die before birth.
In dogs, lethal genes usually cause homozygotes to die soon after birth.. F. Hutt (1979) showed the action of the “bird tongue” gene: puppies homozygous for it have a slight defect in the shape of the tongue, but because of this they are not able to suck milk and die from exhaustion in the first days of life.
Not everyone flew cause immediate death of puppies immediately after birth: it can occur at the age of several months or even years. This type includes many genes that affect the nervous system. Others, such as the hemophilia gene, can occur both at birth and be of the “delayed action” type. A hemophilic puppy may die from bleeding due to accidental injury.
Hemophilia, whose gene h is located in the sex X chromosome, is most often manifested in males — they have the HNU genotype, receiving the hemophilia gene from mothers carrying it. Female carriers of the ХHХh genotype are phenotypically normal, but half of their sons will inevitably be hemophilic. The conclusions for breeders are clear: when encountering such an anomaly, not only sick males (if they survive) should be excluded from breeding, but also all identified female carriers.
Cryptorchidism is similarly inherited.. Although it is not lethal, it significantly reduces the reproductive abilities of males (with unilateral critorchism) or entails complete infertility (with bilateral). Cryptorchidism is a sex-related trait. Its recessive gene c is located on the X chromosome. Phenotypically this defect appears in males (genotype Xc Y). In the transmission of cryptorchidism, the role of male unilateral cryptorchids of precisely this genotype is most noticeable, which is also reflected in the “Regulations on pedigree work.” Prohibiting the use of descendants of male cryptorchids in planned breeding. However, no less dangerous for the breed of the female carrier of the gene c. They, both hetero- and homozygotes (the disease does not manifest themselves in them), are capable of transmitting this gene to descendants, which is why it is not necessary to use female gene carriers of cryptorchidism with breeding producers.
Subblets (semi-lethals) are called genes that cause a wide range of changes in the body, poor health and sometimes death. Thus, cyclic neutropenia is caused by the recessive cn gene (Robinson, 1982). Homozygotes grow slowly on it and usually die from infectious diseases, which they lack resistance to due to the presence of this gene. Therefore, the sublet cn, although it does not seem to be the direct cause of the death of dogs, is actually directly related to it.
Since recessive abnormal genes are still not common in rocks, they usually spread by binding of heterozygous carriers (phenotypically normal) to normal homozygotes. Puppies born in this case are also outwardly normal, but half of them will again be carriers of a mutant gene that remains masked in the breed, and thus is transmitted from one generation to another, to the third, etc. in a hidden form. In fact: each animal, as you know, each gene is in duplicate (in a pair of homologous chromosomes). Therefore, with the number of one generation of the breed of dogs n, the total number of each specific gene in the generation will be 2n. If in this generation the frequency of the anomaly gene is equal to X, then with free crossing, the probability of combining two abnormal genes in the same genotype is equal to the product of the frequencies, i.e., ХХХ = X2. So, at a frequency of X = 0.01 (one out of a hundred), the probability of having a puppy with manifestations of anomaly will be 0.01 2 = 0.0001. In other words, only one puppy out of ten thousand born will be defective. With such a low probability, if an anomaly is detected, there is no reason to suspect it as a genetic one. Therefore, even if there is a struggle to eliminate the anomaly, the decrease in the prevalence of abnormal gene carriers in the breed is very slow. Indeed, the corresponding gene is preserved in the population of these carriers in a disguised form, and culling of carriers is difficult, although it can, if successful, improve the line or breed.
Pets practically do not cross freely, i.e., haphazardly. Here, the reason for the relatively widespread occurrence of some anomalies is in the inbreed structure, in line breeding, when the influence of the ancestors plays an important role. If they turn out to be heterozygous carriers of an abnormal gene, inbreeding of their heredity will cause an anomaly in the descendants, as a rule, 2-3 generations later. At the same time, the role of male dogs producing numerous offspring is especially great, which can complicate the situation and contribute to the mass distribution of undesirable traits (this happens in the absence of a competent and timely selection analysis).
We can refer to the unsuccessful experience of using a German (East European) shepherd dog, the champion of the Novosibirsk dog shows Mangush K-510 (Vlad. Timofeev) in the Novosibirsk club of service dog breeding in the Novosibirsk club of service dog breeding. Mangush was used very widely as the main successor in Novosibirsk to the line of champion Ingul K-1 (Vlad. Golovanov). As it turned out later, Mangush passed the cryptorchidism genes to descendants, and after some time the Mangush genealogy line degraded.
However, the correct work with manufacturers allows expanding the possibilities of selection for elimination of such anomalies - because the intensity of selection among males (breeding differential) can be especially high.
Of course, the already noted role of the ancestors most widely used in breeds is great in the distribution of anomalies, as well as in general hereditary traits. However, one should also take into account the patterns of manifestation of variability in related species or animal breeds due to the famous law of homologous series in hereditary variability, discovered by academician N. I. Vavilov. The meaning of this law is that genetically close species, genera, or breeds are characterized by series of hereditary variation with such correctness that, knowing a number of forms within one species (or, in our case, one breed), one can predict the presence of similar forms in others species (breeds). The closer these species or breeds are by origin, the more complete the similarity is in the ranks of their variability.
This law is widely used by breeders in the development and improvement of new varieties and breeds, and it is unfortunate that among dog breeders have not yet received the necessary recognition as a method of studying hereditary variability and a tool for breeding.
An example of the combined effect of the influence of the ancestor and the law of N. I. Vavilov is the recent case from the expert practice of the author. At the Novosibirsk brood of young animals in 1987, two puppies were present in the litter of Giant Schnauzers along with pedigree parents and most of their descendants, who were left atypical for the breed according to the results of the inspection in accordance with the rules “without assessment”. Their coat was intermediate between wire-haired and short-haired with a deviation in the direction of short-haired. The color of the puppies is black with brown smeared and irregular tan markings. The litter was received inbreeding to the famous Moscow producer Aike-03420 (Vlad. Proklova). Analysis of breed breeding showed that this selection has repeatedly caused the appearance of puppies with atypical coat color and coat. There is, of course, the influence of the ancestor - the bearer of "harmful" genes. However, the law of N. I. Vavilov is also manifested here. It is known that all breeds of Schnauzers - Riesen, Mittel and Zwerg - are closely related to their shorthaired late relatives by Pinscher breeds, making up the whole variation series with the latter. The type of coat and tan color are characteristic pedigree signs of pinschers. In the case under consideration, it was they, by virtue of the law of homologous series, that "split out" in the litter of rizenschnauzers.
The complex of the two mechanisms under consideration is valid in the following example. Nowadays, the position of genetics on the non-inheritance of the so-called acquired characters is already non-debatable. For example, tail docking - a mandatory procedure for a number of dog breeds - has been carried out for many years. And no matter how many generations are subjected to stopping, puppies are still born tailed. This is the manifestation of one of the fundamental laws of genetics.
Sometimes in litters among puppies born with tails of normal length, bobtail tails appear. And in this case there are no exceptions to the laws of genetics. Professor N. A. Ilyin (1932) and A. P. Mazover (1947) also reported such scanty Dobermann puppies. They convincingly explained that the cob-tail is anatomically different from those tailored in accordance with the tail standard. The short tails of Dobermans are pear-shaped, and the last vertebra is an irregular flattened structure. This trait is inherited by Dobermans from Rottweilers. An interesting observation by A.P. Mazover that Dobermans with congenitally shortened tails was also distinguished by a wide-bodied massive Rottweiler-type physique. Subsequent breeding of the breed to obtain lightweight elegant dogs eliminated not only this type of physique, but also contributed to the almost complete disappearance of congenital short-tail tail among Dobermanns. This result of the process of breed formation is also interesting as a manifestation of indirect selection, when selection and selection are carried out according to one specific characteristic, but in the end they affect, due to complex genetic mechanisms (and sometimes quite unexpectedly for breeders), other qualities of the breed.
A necessary element of breeding is the registration of puppies with signs of anomalies and analysis of accumulated material. If the pedigrees of abnormal puppies of the clichés of certain manufacturers are repeated, carriers of mutant genes can be established and the mating plan corrected.
Elimination of anomalies in the breed, plant line or genealogical group is carried out depending on the type of its inheritance. With the dominant monogenic type, the scheme is clear: the exclusion from the mating plans of all individuals with manifestations of anomalies. Of course, there are complicated cases - with incomplete penetrance of the dominant gene, then carriers can be established after detecting abnormalities in their puppies. To establish which of a pair of parents is guilty of the transmission of hereditary violations, each of them should be tied with other partners from whom the appearance of such an anomaly is not registered.
Recessive anomalies can be selected in two ways. The first of them is similar: to exclude dogs with manifestations of abnormalities, i.e. homozygotes, from breeding. The occurrence of anomalies during such selection in the first generations decreases sharply, and then more slowly, remaining at a relatively low level.
The reason for the incomplete elimination of some anomalies even during a long and persistent selection is, firstly, a much slower reduction in the carriers of recessive genes than homozygotes. Secondly, in the case of mutations that slightly deviate from the norm, breeders do not always reject abnormal dogs and carriers.
Thus, an absolutely complete elimination of the anomaly is fundamentally possible provided that all carriers are detected. The scheme of this identification: heterozygotes for recessive mutations can in some cases be detected by laboratory research methods. However, for genetic identification of heterozygous carriers, it is necessary to carry out analyzing crosses - mating a dog suspected as a carrier with an abnormal homozygous (if the anomaly slightly affects the body) or with a carrier that has already been established. If, as a result of such crosses, abnormal puppies are born among others, the tested producer is unambiguously defined as a carrier. However, if such puppies are not identified, then an unambiguous conclusion cannot be drawn on a limited sample of the obtained puppies. The probability that such a producer is a carrier decreases with the expansion of the sample - an increase in the number of normal puppies born from mating with him.
A special group of anomalies, for example, known in recent years in wide circles of domestic dog breeders, hip dysplasia, does not have the monogenic nature of inheritance, which was still discussed, but polygenic. The control here is carried out by a whole complex of recessive and dominant genes that make a correspondingly smaller or larger contribution to the phenotypic manifestation of the trait. Depending on the combination of such a complex of genes in the genotype, the degree of manifestation of the anomaly in different dogs can be very different.
In the course of selection for elimination of polygenic anomalies, ideally (in practice unattainable) all individuals with any, even the weakest degree of manifestation of the anomaly should be rejected, however, only animals with the most significant deviations from the norm are most often excluded from breeding, Weak deviations, especially in dogs, on other grounds it is very valuable in tribal terms, they are not considered the basis for culling and only taken into account when selecting partners for them. This usually explains the long-term selection against polygenic anomalies.
Even more difficult is the fight against anomalies of the threshold type of inheritance. In principle, this is the same polygenic inheritance, but in this case, the phenotypes do not manifest the entire diversity of genotypes with different combinations of polygenes. Anomalies of this type manifest themselves only in dogs, in the genotype of which the number of “dominant” polygenes (contributing to the formation of the trait) reaches a certain critical limit, that is, a threshold. The breeding policy is similar to that in which the breeder confines himself to the rejection of animals with the most pronounced polygenic anomalies (in the latter case, with manifestations of anomalies of threshold inheritance in the phenotype), leaving dogs with insignificant manifestations on the tribe. With threshold inheritance, it is impossible to determine and reject by the phenotype of dogs in which the set of polygenes does not reach the threshold for the manifestation of anomalies. But when it becomes known that certain outwardly normal producers give children with manifestations of threshold type anomalies, the question of limiting their breeding activity or, if the percentage of abnormal offspring is high, the exclusion of such dogs from the production line may be decided.
According to the threshold type, for example, deviations in the structure of the dental system are inherited: absence of one or more premolars and molars. Therefore, as a result of some selections even of full-toothed parents, combinations of genes can form in the genotypes of their children, which caused the absence of one or several in different combinations of teeth. Naturally, the likelihood of giving birth to non-toothed puppies increases dramatically if at least one of the parents himself contains a threshold set of polygenes and is not-toothed.
Here it should be noted the full validity of the requirements of the Regulation on breeding work with breeds of service dogs on the inclusion in the plans of breeding only dogs with full dental formulas. Indeed, from the standpoint of genetics, it is important not only that a complete set of teeth is in itself necessary for a healthy and efficient dog. It is also significant that gnarliness indicates possible homozygosity not only for the genes of this trait, but also for many other genes, among which there can almost certainly be genes of various sublets and anomalies that cause a general weakening of the body and loss of constitutional strength - phenomena, in principle similar to inbred depression.
Thus, any deviations from the complete dental formula should be considered as an indicator of an undesirable combination of gene blocks in the genotype, which can lead to a decrease in the strength of the constitution, and must be subjected to strict selection. It is necessary not only to cull the non-toothed dogs, not allowing them to mate, but to carefully analyze the breeding use of their parents so as not to repeat the selection scheme that results in the non-toothed puppies. In the fight against polygenic anomalies in comparison with individual selection, without replacing it, group selection (family) is more effective. The decision on the breeding use of close relatives of those dogs in which such anomalies are found should be made in accordance with specific conditions and conditions. It is necessary to take into account the value of these animals in tribal terms, the danger of anomalies for the breed, its prevalence and genetic knowledge.
Source: S. P. Knyazev, Candidate of Biological Sciences, "Service Dog Breeding" 1989
Against the recessive gene
A very complex type of selection that requires monitoring over several generations. And the more there will be, the better for the work of breeders. According to official reports, the selection of dogs through this selection is a rejection of not only recessive homozygous animals, but also their heterozygous ancestors (in our case, we are talking about parents). It becomes obvious that the method is very long and requires exclusive control over the resulting offspring and its parents.
As a result, he got such dogs as Mexican hairless, collies, dogs and dachshunds. Selection is carried out in the case when the breeder decides to obtain individuals with superdominant genes. As a result of this dominance, unusual marble colors are obtained, or, under the influence of the lethal gene, animals with no hair.
It is used quite rarely, only when working with some dog breeds. One of them is poodles. For example, it is necessary to obtain offspring of silver color. Most members of the breed have a dark gray color, which is formally considered as silver. But this is the wrong approach: such individuals must be discarded from breeding dogs with a silver true color.
Thus, such selection in dog breeding is used when heterozygotes have a phenotype or complementarity that is completely undesirable for certain individuals.
Talk about breeding
Dog breeding and breeding are quite complex things that require very deep knowledge from the breeder (breeder). But if artificial selection and heredity are mentioned above, then one cannot but mention breeding methods. Let's get very brief about this.
There are two methods: interbreed and purebred. For the breeding of new animals, the first method is used, for fixing one form or another within the breed, of course, a purebred breeding method is used.
Pure breeding can be unrelated (outbred), inbred (sibling), linear and interline (outcross).
If you do not go into all the details, but speak briefly, then outbred breeding is a mating of animals that are not related. In other words, in their pedigrees there are no common ancestors even in the most distant generations. Now outbred breeding is very popular: local bitches are knitted by foreign export dogs. The resulting daughters are again knitted with imported males, and so on from generation to generation.
Representatives of the male breed obtained as a result of this breeding method rarely take part in mating.
This is a closely related crossing, used to consolidate certain qualities, as well as the exterior of the breed. They are often used, but not always the desired result is obtained as expected. The method is dangerous in that you can get not only an outstanding dog, but also a complete freak. But one cannot deny that inbred breeding has always been used to obtain clean lines.
There are several degrees:
- Close inbreeding: mating between father and daughter, mother and son, half-bibs, brother and sister, grandmother and grandson, granddaughter and grandfather.
- Close relationship: for both dogs that are going to be knitted, there is a common ancestor in the fourth generation.
- Moderate kinship: the presence of a common ancestor in IV-VI generations.
These are the basics of dog breeding. Described here is quite superficial, it serves only as a material for acquaintance and expansion of one's own horizons.
Of course, those wishing to engage in dog breeding must be familiar with the basics of genetics and understand how alleles differ from genes. Currently, only a person with a higher cynological education can officially register his own nursery.