More to it than meets the eye.
-By Dr.H.J.Hewson-Fruend BA (Prof Writ.) BSc (Hons) PhD (Syd)-
A pedigree, by definition is a genealogical table or ancestral line. The genealogical table, or family tree, lists descendents of given parents; an ancestral line lists the ancestors of a given individual. As a generalization, the dog world only uses the ancestral line form of pedigree. At face value, the pedigree is little more than an organised list of names. It will tell you which animals have gained a championship in the show ring, which animals were imported, and which animals are related.
However, it tells you nothing about the individuals apart from their sex. It is necessary to have a whole range of additional information about the individual dogs before a pedigree can take on much meaning. Even then, the value of ancestral line pedigrees is over-rated. They give the false impression of heritable contribution from ancestors. Consequently, breeders assume more information from them than is valid.
THE NUMBER OF ANCESTORS
A 4-generation pedigree has 30 ancestors; a 10-generation pedigree has 2,046 ancestors; a 20-generation pedigree has 2,098,150 ancestors and a 30-generation pedigree has 2 billion ancestors. If the dog has a 2 year generation length, the pup with the 30-generation pedigree had approximately 2 billion ancestors running around about 60 years ago. This is nonsense. It is nonsense because the structure of an ancestral line pedigree is misleading. A genealogical-table pedigree is much more valid. It is structured according to reality, but it can become extremely complex if all mateings and all descendents are included.
Breeders indulge in in-breeding in order to increase levels of homozygosity - to increase the levels of pure breeding for given desired qualities. So-called prepotent animals are thought to have high levels of homozygosity. Unfortunately, in-breeding leads to homozygosity for undesired qualities as well as desired qualities. It also leads to in-breeding depression. Hence successful breeding involves a balance of selection against (and a tolerance of) problems versus relatively close in-breeding. It is known as line-breeding. For example, cousin to cousin; nephew to aunt; and uncle to niece mateings are known as line-breeding. This means that the ancestral-line pedigree has a large number of common ancestors on it. Hence a 30-generation ancestral-line pedigree has far fewer unique ancestors than 2 billion !!!
THE DEGREEOF INHERITANCE FROM ANCESTORS
Breeders attempt to have famous dogs appear in their pedigrees. They trust that these dogs will contribute to the quality of progeny bred in their kennels. Galton's Law of Ancestral Inheritance has helped to reinforce their trust. The law assumes that each pup gains 50% of its total inheritance from each parent; 25% from each grand-parent; 12.5% from each grand-parent and so on. This is usually estimated in terms of percentage "blood". In reality, it is only correct for the first generation. Beyond that, due to the way genetic material is assorted during meiosis, the law becomes increasingly inaccurate per generation (unless large populations, rather than specified dogs, are under investigation.)
In interpreting a pedigree, it should be born in mind, that it is genes that are inherited, not qualities..Consequently, two blue Australian Cattle Dogs can produce red pups. Moreover, the capacity to produce chocolate pups may go unexposed for generations, or conversely, be lost. The implication is that a particularly great dog ancestor may have passed on a given quality that is undetected for a few or several generations. Similarly, a known carrier of a given quality may have failed to pass that quality on to his descendents on the pedigree. A genealogical-table pedigree, which includes all mateings and progeny, will reveal more of the genetic make up of a particular ancestor. The probability of revealing segregation for a given quality, say red, is increased.
LINE-BREEDING IS NOT WHAT IT APPEARS
Each unique ancestor will have a particular probability of contributing a particular allele. However, the same does not hold for the ancestors of common ancestors. If the subject of our pedigree has a common grandsire/dam, the proposition that the grandsire/dam's parents will provide more than one contribution is invalid. This is best understood using a genealogical-table. It means that each individual, depending on how in-bred it is, may have very few unique ancestors in its recent ancestry. e.g.,A 4-generation open pedigree(no common ancestors)has 30 ancestors. A brother/sister mateing has 16 ancestors and a cousin/cousin mateing has 24 (assuming that they had no common ancestors). it also means that the appearance of a particular ancestor more than once on a pedigree, may lead to false expectations of its contribution to your pup. For example; If the common grandsire referred to above, had a famous sire, that sire would appear on both sides on the pedigree - good line breeding!! But, in reality, that great grandsire has made one genetic contribution only. Thus, the so-called good line-breeding was on the common grandsire only.
Some breed clubs are now indulging in pedigree judging at some of their specialty shows. In effect, the best exemplars, using traditional conformation assessment based on their pedigree. The basis for this is that "blood" is of greater importance than the animal. It is assumed that an outstanding specimen with a mediocre pedigree, may be outstanding due to chance or a favourable environment. Furthermore, since an animal can only pass on a 50% sample of its genetic information (not a specific combination), it may not be a good sire or dam. The corollary is that an outstanding animal with an excellent pedigree will be a good sire or dam (it will be more homozygous or more prepotent). At best, this is a form of praising the progeny tested ancestors of the subject of the pedigree. At worst, it is full of fallacies, some of which are noted above.
In addition, the [pedigree takes no account of external factors. To quote Willis(1976),"A poor specimen is not improved by possession of a prestigious pedigree, though a very badly-reared animal may be genetically better than he looks".
Moreover, the runt litter-mate posses the same pedigree as the outstanding specimen, reminding us that their parents passed on vastly different combinations of genetic information. to compound this, some pedigrees are falsified and do not state who all of the ancestors really are.
The determination that a particular pedigree is excellent is based on the performance of ancestors on the pedigree. That performance is estimated from both the quality of the dog and the quality of its progeny. Progeny testing is most successfully carried out on males, because they can sire large numbers of progeny, where bitches are restricted in that way. To be done effectively, a large and popular breed is necessary. Its success is dependant on a large number of artificial factors; choice/availability of quality bitches; breeders providing optimum conditions for pups to grow in; unbiased and competent assessment of the progeny, etc.
In itself, progeny testing leads to an unjustifiable bias against 50% of the genetic contribution - that of the bitch. What perforce is overlooked is the fact that if a line of prepotent males is to be maintained (e.g., all EE) then not only must the sire contribute E to all and every pup, but also the dam must contribute E also. When the pedigrees of the progeny of a given sire are thus rated for pedigree judging, the inherent bias follows. Logically, the only animals on the pedigrees that will be rated as being in any way significant, are the great producing sons of sons of sons etc.i.e., the top (outer) row(line) sires, because they themselves have been progeny tested. This bias is reinforced by kennels striving top established lines of great animals from father to son to grandson etc., but as has been pointed out by Willis (1989),"this line, 9 the tall line) is no more important than any other line/s in the pedigree."
The conclusion must be that ancestral-line pedigrees have limited value to breeders when analysing or planning breeding programs. Genealogical-table pedigrees are much more practical and reliable. Moreover, breeders must check out claims made about inheritance based on the animals appearing on pedigrees. Many of the claims will prove to be biased(at best), or even erroneous (at worst).
"Inbreeding for the sake of producing offspring that look like their parents is a crime against nature"