# Outcrossing



## pitbullmamanatl (Jun 1, 2010)

*OUT CROSSING
By Scot E. Dowd Ph.D.
Outcrossing brings together two APBTs that are less related than the average for the breed. By convention both the sire and dam during an outcross should have some linebreeding in their background because no matter how you slice it, breeding a scatterbred dog to a linebred dog produces a scatterbred dog (see our case study below). Many breeders feel this is outcrossing but in reality you now have only half your lines genes and no rational idea what the other half may be. Thus we usually consider outcrossing to involve two linebred or inbred animals from different bloodlines.

A reason to outbreed would be to bring in new traits that your breeding stock does not possess or to decrease the inbreeding coefficient or typically both. When you are looking for high quality traits, also termed aptitudes, that are not present in acceptable members of your germline, then the most obvious way to bring in missing aptitudes is to outcross to a line prepotent for these. Thus, if you are experiencing inbreeding depression you can seek dogs outside your lines with aptitudes that compliment your lines weaknesses. Example one would choose a mate that does not possess the same faults while phenotypically complements and hopefully maintains your dog's good traits. By convention both individuals should be linebred but share no common ancestors in 5 generation pedigree. This promotes more heterozygosity, and gene diversity within each dog by matching pairs of unrelated genes from different ancestors. Note that the key type genes that define our breed will always stay paired. Unfortunately, outbreeding can also mask the expression of recessive genes, and allow their propagation in the carrier state.

When the sire and dam may be genetically unrelated especially compared to your linebred dogs you may experience yet another outcross phenomenon known as heterosis. Heterosis is more commonly called by APBT breeders as hybrid vigor. It should be noted that hydrid vigour is more commonly used to describe mixing of different species rather than different breeds of course but it is still an apt term. What we notice sometimes when we do logical complimentary outcrosses among our breed is a burst of fertility, good health and growth that is seen in the progeny when two unrelated germlines are mated. The more divergent and unmixed these unrelated germlines are the greater the differences between them and ultimately we will see more evidence of hybrid vigour as we revert to heterotrophic on many alleles that cause Inbreeding depression. Allelic diversity is a good thing in many instances even though we try when producing a germline to pair up on many others. We must always avoid inbreeding depression especially if our lines are becoming less healthy.

What we seek with an outcross similar to phenotypic complementarity is to overcome defects in one or other germline - the way two bloodlines "nick" or really "mix well" in dog breeding terms." On the other hand breeders are often turned off from outcrossing especially novice breeders because there is always a risk involved and careful and longterm goals must be established and short term problems anticipated and prepared for. Outbreeding can produce exceptional quality in the F1 generation or can produce nightmares (just like Inbreeding huh?). We must carefully analyze if we can obtain from each outcross that which we are seeking and avoid bringing in those traits we cannot easily get rid of if they end up set within out lines. This is why many outcrosses fail. Contrasting aptitudes of specific germlines can definitely conflict with one another, rather than blend. However, with the APBT when we are selective for specific traits during outcrossing that are both favorable and if we also select against as many unfavorable genes as possible, the shared genetic background of the strains or homozygosity of so many alleles will help contribute to a favorable blend of their contrasting aptitudes especially as outcrosses are blended back into the germlines logically.

Outcrossing Depression (the flip side)
In some cases, inbreeding is purposely done to create a "pure line" of individuals which all have similar genes. This is the case with many lines of APBT. Breeders intentionally linebreed to create a population that has the genes for desired traits in a homozygous state, so that the offspring will perpetuate the desired phenotype. Over generations, individuals with deleterious genes are removed from the breeding population, resulting in a monomorphic, yet healthy population. (OK it is possible) These populations can actually suffer "outcrossing depression" when crossed to unrelated individuals which results in new combinations of alleles, and possible entry of deleterious genes.
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