Wednesday, August 12, 2009
Inbreeding, Line-breeding and Outcrossing
3:38 PM | 
Posted by
Rachelle Tarango
Inbreeding
Line-Breeding
This is a more broad type of inbreeding which conserves valuable characteristics and in a general sense, gives us some control over type and in a lesser control over specific characteristics. It creates "strains" or "families" within a breed which are more easily recognized by their similar conformation.
Specifically, line-breeding entails the selection of breeding partners, who have within their pedigrees one or more common ancestor. These individuals occur repeatedly within the first four or five generations so that it can be assumed their genetic influence molds the genetic type of succeeding generations. It is a fact that in many breeds, success has been obtained by line-breeding to outstanding individuals.
One of the chief dangers of line-breeding can be contributed by the breeder of one strain. Many times the breeder reaches a point where he selects potential breeding partners based on pedigree alone, instead of individual selection and pedigree combined, within the line.
Outcross Breeding
Outcross breeding is the selection of breeding partners whose pedigree, in the first five generations are free from any common ancestor.
For the breeder to exercise any control over the progeny of an out-cross mating, one of the partners should be inbred or closely line-bred. The other partner should show in himself and in the progeny test when bred to other mates, that he is dominant in the needed compensations which are the reason for the out-cross. Greater uniformity can only be achieved if the out-cross is made with animals of similar family type.
To summarize, we find that inbreeding brings us a fixity of type and simplifies the breeding formula. It strengthens desirable dominants and brings hidden and undesirable recessives to the surface where they can be recognized and possible culled and corrected with out-cross breeding. When we have established a definite improvement in overall type by rigid selection for desired characteristics, we line-breed to create and establish a strain of family line which, in various degrees, incorporates and produces the improvements which we have worked to produce.
By breeding father to daughter, half-brother to half-sister, son to mother, and by the closest inbreeding of all, brother to sister, stability and purity of inherited material is obtained. Specifically, inbreeding focuses on both desired features and faults, strengthening dominants, and bringing recessives out in the open where they can be seen and evaluated. This selective process supplies the breeder with the only control over prepotency and homozygosity. Inbreeding does NOT produce degeneration of a line: It merely concentrates weakness already present, so they can be recognized and eliminated within a line.
It is essential that the breeder have complete understanding of the merits of inbreeding for by employing it skillfully results can be obtained to equal those of other successful animal breeding programs. You must keep in mind that inbreeding itself creates neither faults or virtues, it merely strengthen and fixes them in the resulting animal. If the basic stock used within a line is generally good, possessing few if any minor faults then inbreeding will concentrate all those virtues which are so valuable in that basic stock. Inbreeding gives us great breeding worth by its unique ability to produce prepotency and unusual similarity in predicting more similar type. It exposes the "skeletons" in the closet by bringing to light hidden faults within a line so the breeder is able to select against it.
Line-BreedingThis is a more broad type of inbreeding which conserves valuable characteristics and in a general sense, gives us some control over type and in a lesser control over specific characteristics. It creates "strains" or "families" within a breed which are more easily recognized by their similar conformation.
Specifically, line-breeding entails the selection of breeding partners, who have within their pedigrees one or more common ancestor. These individuals occur repeatedly within the first four or five generations so that it can be assumed their genetic influence molds the genetic type of succeeding generations. It is a fact that in many breeds, success has been obtained by line-breeding to outstanding individuals.
One of the chief dangers of line-breeding can be contributed by the breeder of one strain. Many times the breeder reaches a point where he selects potential breeding partners based on pedigree alone, instead of individual selection and pedigree combined, within the line.
Outcross Breeding
Outcross breeding is the selection of breeding partners whose pedigree, in the first five generations are free from any common ancestor.
For the breeder to exercise any control over the progeny of an out-cross mating, one of the partners should be inbred or closely line-bred. The other partner should show in himself and in the progeny test when bred to other mates, that he is dominant in the needed compensations which are the reason for the out-cross. Greater uniformity can only be achieved if the out-cross is made with animals of similar family type.
To summarize, we find that inbreeding brings us a fixity of type and simplifies the breeding formula. It strengthens desirable dominants and brings hidden and undesirable recessives to the surface where they can be recognized and possible culled and corrected with out-cross breeding. When we have established a definite improvement in overall type by rigid selection for desired characteristics, we line-breed to create and establish a strain of family line which, in various degrees, incorporates and produces the improvements which we have worked to produce.
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