In-Breeding in Dogs – A Detailed Review

  1. Introduction. The diversity of domesticated dogs is an example of the power of artificial selection. All breeds share common ancestry, having descended from wolves. Humans selectively bred them to enhance specific characteristics, such as colour and length or body size. This created a range of breeds that include the Chihuahua, Great Dane, Basset Hound, Pug, and Poodle (ranging to more than 270 recognised breeds). Wild wolves, which did not undergo artificial selection, are relatively uniform in comparison.
  2. Types of Dog Breeding
    1. In-Breeding. In breeding is the mating of very close relatives, for example, father to daughter, half-brother to half-sister, brother to sister, mother to son, etc. In breeding intensifies the faults as well as the strong points, so considerable discretion must be used in the choice of the dogs. The faults may be to such an extent, that, sometimes, entire litters have to be destroyed in cases where obvious anomalies occur. For this reason, this type of breeding is not recommended to novice breeders. Sometimes, in-breeding is the only option available, for example, in the re-creation of a nearly extinct breed or in breeding programs of newly created breeds.
    2. Line-Breeding. Line breeding is the mating of dogs having many common ancestors or mating to a slightly removed relative, e.g. granddaughter to grand sire, uncle to niece, etc. The benefit of line-breeding is the production of more consistent litters. In order to have a chance to reinforce desired characteristics and eliminate health problems one has to have a thorough knowledge of both pedigrees of both the sire and the dam for at least five generations. In general, most breeders adhere to a policy of line breeding, whereby they can assure uniformity of quality without risking the inherent dangers of in breeding. This technique appears to be the best compromise between in breeding and the doubts of out crossing or out breeding.
    3. Out Crossing. Out crossing is the mating of two dogs that are the products of line breeding but of two distinctly separate lines. Unless the two dogs involved in an out cross are strongly line bred with a possibility of a certain measure of prepotency, uniformity to the first generation is generally doubtful. It is generally employed as a long-term proposition to bring certain traits into a line that are otherwise deficient. These traits then need to be intensified by proper line breeding or in breeding.
    4. Out Breeding. Out breeding is the mating of two dogs who not only are the products of two distinctly separate lines, but on top are not the products of line breeding. Out breeding is seldom employed since in most breeding programs dogs that would qualify for out breeding simply do not exist. In summary, most successful breeders use some formula involving general line breeding with in breeding employed when sufficiently outstanding products of their line result and out crossing only when another line can supply a strong characteristic in which they are lacking.
  3. In-breeding Depression. In breeding is the reproduction from the mating of two genetically related parents, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is called in breeding depression.
  4. Culling. Deleterious alleles causing in breeding depression can subsequently be removed through culling, which is also known as genetic purging.
  5. Results of In-breeding. In-breeding may result in a far higher phenotypic expression of deleterious recessive genes within a population than would normally be expected. As a result, first-generation in bred individuals are more likely to show physical and health defects, including:
    1. Reduced fertility both in litter size and sperm viability.
    2. Increased genetic disorders.
    3. Fluctuating facial asymmetry.
    4. Lower birth rate.
    5. Higher infant mortality.
    6. Slower growth rate.
    7. Smaller adult size.
    8. Loss of immune system function.
  6. Natural Selection. Natural selection works to remove individuals with the above types of traits from the gene pool. Therefore, many more individuals in the first generation of in-breeding will never live to reproduce.
  7. In-Breeding is a Part of Natural Breeding in the Wild. Natural breeding include in-breeding by necessity, and most animals only migrate when necessary. In many cases, the closest available mate is a mother, sister, grandmother, father, grandfather. In all cases the environment presents stresses to remove those individuals who cannot survive because of illness from the population.
  8. Dominant Males / Alpha Dog Concept. In wolves (or wild dogs) prides are often followed by related males in bachelor groups. When the dominant male is killed or driven off by one of these bachelors, a father may be replaced with his son. There is no mechanism for preventing in-breeding or to ensure out crossing. In the prides, most females are related to one another. If there is more than one dominant male, the group of alpha males are usually related. Two lines then are being “line bred”. Additionally, the alpha males of two neighbouring prides can potentially be from the same litter; one brother may come to acquire leadership over another’s pride, and subsequently mate with his ‘nieces’ or cousins. However, killing another male’s cubs, upon the takeover, allows for the new selected gene complement of the incoming alpha male to prevail over the previous male.
  9. False Assumption. There was an assumption that wild populations do not in breed; this is not what is observed in some cases in the wild. As described above it is unavoidable in many cases.
  10. Calculation of Coefficient of relationship. The in-breeding is computed as a percentage of chances for two alleles to be identical by descent. This percentage is called “in breeding coefficient”.
  11. Assuming no previous in breeding between any parents, typical in-breeding percentages are as follows:-
    1. Father/daughter, mother/son or brother/sister: 25%
    2. Grandfather/granddaughter or grandmother/grandson: 12.5%
    3. Half-brother/half-sister: 12.5%
    4. Uncle/niece or aunt/nephew: 12.5%
    5. Great-grandfather/great-granddaughter or great-grandmother/great-grandson: 6.25%
    6. Half-uncle/niece or half-aunt/nephew: 6.25%
    7. First cousins: 6.25%
    8. First cousins once removed or half-first cousins: 3.125%
    9. Second cousins or first cousins twice removed: 1.5625%
    10. Second cousins once removed or half-second cousins: 0.78125%
  12. Definition of Allele. An ‘allele’ is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome. These DNA coding determine distinct traits that can be passed on from parents to offspring. The process by which alleles are transmitted was discovered by Gregor Mendel and formulated in what is known as Mendel’s law of segregation.
    The gene for seed shape in pea plants exists in two forms, one form or allele for round seed shape (R) and the other for wrinkled seed shape (r). Organisms have two ‘alleles’ for each trait. When the alleles of a pair are heterozygous, one is dominant and the other is recessive. The dominant allele is expressed and the recessive allele is masked. Using the previous example, round seed shape (R) is dominant and wrinkled seed shape (r) is recessive.
    Round: (RR) or (Rr)
    Wrinkled: (rr)

13. An in breeding calculation may be used to determine the general genetic distance among relatives by multiplying by two, because any progeny would have a 1 in 2 risk of actually inheriting the identical alleles from both parents.

14. For instance, the parent/child or sibling/sibling relationships have 50% identical genetics.

15. For siblings, the degree of genetic relationship is not an automatic 50% as it is with parents and their children, but a range from 100% at one extreme, as in the case of identical twins (who obviously cannot mate as they are the same sex), to an exceedingly unlikely 0%. In other words, siblings share an average of 50% of their genes, but unlike the 50% ratio between parents and children, the actual ratio between siblings in any given case can vary.

16. Near Cloning in Pet Dogs. An intensive form of line breeding where an individual with highly desirable traits (S) is mated to his daughter (D1) and granddaughter (D2) and so on, in order to maximize the percentage of S’s genes in the offspring. The D3 offspring would have 87.5% of his genes, while D4 offspring would have 93.75%. Such breeding methods can be used to create a “near clone” of a desirable individual. D5 offspring will be a near clone of ‘S’.

17. Assortative Breeding. Breeding in domestic Dogs is ‘assortative breeding’ primarily (or selective breeding). Without the sorting of individuals by trait, a breed could not be established, nor could poor genetic material be removed.

18. Homozygosity

  1. Homozygosity is the case where similar or identical alleles combine to express a trait that is not otherwise expressed (recessiveness).
  2. In breeding, through homozygosity, exposes recessive alleles. In breeding is used to reveal deleterious recessive alleles, which can then be eliminated through assortative breeding or through culling.

19. Use of In-Breeding. In-breeding is used by breeders of domestic dogs to fix desirable genetic traits within a population or to attempt to remove deleterious traits by allowing them to manifest phenotypically from the geno types.

20. Responsibility of Breeders. Breeders must cull unfit breeding suppressed individuals and/or individuals who demonstrate either homozygosity or heterozygosity for genetic based diseases. Problems come up from casual breeders who in breed irresponsibly.

Conclusion. As I always say that betterment of dogs is hidden in, ‘being a responsible dog owners’. So if dog breeders are responsible ones then we can fight all types of unavoidable ills occurring due to any type of breeding. Breeders just need to be sincere with the cause and dog. We need to strike a balance between an effort of achieving a ‘near clone’ of a desired specimen and avoiding the combination of alleles producing genetic ills, faults and harmful health issues for dogs as a species.

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