Methods of Breeding What is outcrossing? Outcrossing is where the sire and dam are totally unrelated, preferably for three or four generations. The true form of an outcross is between two entirely different breeds because in reality the members of most registered breeds come from a common ancestor (although it may be many, many generations back). It is very rare for outcrossed puppies to be uniform in appearance. Usually there are a very large ranges of sizes, coats, colors, markings, and other distinctive characteristics. Outcrossed litters are generally heterozygous, and do not reliably reproduce themselves, so even the nicest puppy in the litter may not later produce the best puppies. Outcrossing is generally used to introduce something new to a line -- a better head, better colors, better front, etc. Usually the puppies retained from these breedings are bred back into the breeders original line to standardize them back into the lines general characteristics and reproducibility -- with the one desired characteristic. The tricky part is that other characteristics may come along for the ride! If you are dedicated enough, you can eventually continue breeding by outcrossing alone (but dont expect instant or quick results). You should pick dogs that complement each other well and are similar in general appearance. This is a long hard road to eventually developing a line. Through outcrossing, many health problems can quickly be eliminated (or just as quickly added into your breeding), but usually you do sacrifice some show quality and productibility. You have to remember that dogs that appear totally healthy may be carriers of genetic problems. To find this out, test mating is done to a dog that is affected with the genetic problem (resulting usually in puppies that are both affected and non-affected carriers) or by inbreeding to a related dog that also doesnt show the signs of being affected (usually littermates are used) this will usually result in some puppies free of the problem, some puppies as carriers, and some puppies affected if both dogs carry the problem gene (this is not as accurate as breeding to an affected dog, but you are less likely to have to put all the puppies down). There are variations on outcrossing. A true outcross could be a dog that has totally unrelated dogs bred together throughout the pedigree. This is very rare. On the other hand, linecrossing is a form of outcrossing where dogs from unrelated lines are bred to produce a new line. The sire and dam are usually very linebred from their prospective lines and the resulting puppies are varied in appreance, some looking like the sires line and some looking like the dams line and some looking like mixtures of both lines. How about line breeding? Line breeding is when the sire and the dam are distantly related: e.g., grandsire to granddaughter, granddam to grandson, second cousins, half cousins, uncle to niece, aunt to nephew..... The general strategy is that there is a common ancestor that is being doubled up on both sides. So the desired dog appears several times in the pedigree. This is probably the most common strategy in breeding purebred dogs (and in developing new breeds, for that matter). Though this method, new genes are slowly introduced and unwanted genes are slowly replaced. The actual rate varies by how strongly you line breed. It sacrifices little overall quality in terms of show quality. Usually the puppies are rather close in general conformation. The only problem with this method is that it often takes several generations to get poor genes out, (or adding desired genes in) resulting in many puppies that have the same genetic problems (or virtues) that their parents have. And then because some breeders are more interested in winning, they do not place the affected puppies on spay/neuter contracts. This is both a blessing and a curse for the breed. If the breeder is very careful, affected pups can be used wisely to prevent loss of quality, but still remove the affected genes by only breeding the affected pups to known non-carrier relatives. This way the breeder can again try to edit out the bad genes. It takes longer this way but less show quality is lost in the process. This process results in dogs that will often reproduce their same level of quality. This is refered to as reaching homozygous litters (more genes of the same kind apparent in the puppies). Inbreeding and linebreeding really differ only in degree. Linebreeding is less likely to cause harm than inbreeding. Inbreeding is not for novices. Knowledge of genetics and the breed is required for success. For good results it must be well-planned and breeders must be ready for whatever problems it presents. And inbreeding? Inbreeding is where the sire and the dam are closely related: mother to son, father to daughter, sister to brother, half sister to half brother, cousin to cousin. People disgree about the exact point at which inbreeding becomes linebreeding. Inbreeding is the quickest way to find out what poor genes are in the line and what dominant characteristics are in the line. Although many people are disgusted with the idea of this family incest, it is an extremely useful tool for diagnosing what genes are present. If the genes for bad eyes are present, but hidden or resessive, this will bring them out to their full extent. If there isnt any bad genes, then the puppies will be of very close uniformity and very able to reproduce themselves (theroretically). This is a homozygous breeding. The resulting puppies will have a lot of genetic material that is the same as their parents and grandparents and will be close genetically to each other. Inbreeding doesnt introduce new genes and does not eliminate bad genes that the line already has. It only shifts them around like a rubix cube. This often results in litters with high show potential, if the quality was high to begin with. It shows you what recessives you have lurking in the dogs backgrounds -- both good and bad. But there are drawbacks. Besides the possibility of bad recessives, inbreeding exclusively will eventually lead to infertility. Its like a xerox machine. After so many copies, you have to renew the ink. The same with dogs, you have to introduce new genes. No reputable breeder will use inbreeding exclusively, and many breeders simply never use it. USUALLY, YOU WILL ONLY FIND: VERY EXPERIENCED BREEDERS, IGNORANT BREEDERS, AND PUPPY MILLS MAKING USE OF THIS TECHNIQUE. Inbreeding increases the chance that a gene obtained from the sire will match one obtained from the dam, both stemming from the common ancestor(s) on which the individual was inbred. Thus, inbreeding tends to make animals homozygous rather than heterozygous. The inbreeding coefficient measures the resulting increase in homozygousity. All breeds have a given degree of homozygosity the mating of two dogs from the same breed would not produce a recognizable specimen of the breed! Inbreeding increases homozygosity and decrease heterozygosity. So it can duplicate both desirable and harmful alleles, both of which can be unsuspected in the line, and may appear. Inbreeding does NOT create anomalies, it brings present anomalies to the surface. Even when the anomalies are present, inbreeding might not reveal them. However, once revealed, then the breeder can do something about them in the next generations of breeding. An increase in harmful recessives is undesirable but it is not a major drawback if they are identified early. The effect of inbreeding on major polygenic traits is greater. Generally, traits that are highly inherited (ie largely additively controlled) are not adversely affected by inbreeding but, traits under non-additive control, especially those tied to dominance and thus not of high heritability, are often markedly harmed by inbreeding.
Posted on: Tue, 24 Jun 2014 00:12:48 +0000
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