jack is a very smart men who loves inbreeding and says it is the only way to breed but i can show multiple scientific journal articles that somewhat disagree i recommend everyone go to the site for the institute of canine biology and learn about estimated breeding values and inbreeding coefficients and genetic diversity. no these are not the scientific journal articles i speak of but those can be found on google scholar and some are even about the APBT. now inbreeding coefficients are pretty much useless unless you go back a good number of generations like this site allows.
I will let everyone in on a little secret on why we do not see many inbreeding defects in our working dogs and it has to do with genetic diversity. Now jack is right when he says inbreeding causes nothing but brings out what is already there but he conveniently leaves out that the more you inbreed the less genetic diversity you have when it comes to the genes. now inbreeding/linebreeding is a great tool when used correctly but one cannot inbreed for ever like he says without seeing serious problems.
genetic disorders or traits that are caused by simple recessives can be set or gotten rid of by inbreeding and selecting against or for certain traits but when you have traits good or bad that are polygenic it is not as easy to rid them from the gene pool or set them if they are good
most animal behaviours are caused by polygenic traits for example hunting traits in hunting dogs such as german shorthaired pointers or as i suspect gameness in our dogs.
inbreeding alone does not cause a loss of genetic diversity but inbreeding combined with what is called popular sire syndrome and using only one or two offspring each generation of that popular sire.
take a producer like jeep for example. let's say for example jeep was a carrier of a genetic trait that was not wanted by breeders. now as a carrier he would not express this trait himself. in fact in order for it to be expressed he would have to be bred to another carrier or another dog that expressed it. say this trait was fairly uncommon. then let's say you breed jeep 40 or 50 times like he was and a fairly uncommon trait becomes widely spread throughout the whole line and is almost near impossible to rid the line of this trait add on top of that that say only a couple sons of his were used to breed it would make it even worse thankfully as breeders of the APBT we all have our favorite lines sires dams offspring and the like and our genetic diversity is actually pretty good.
Another thing to study is heredity. now heredity is not that percentage of a trait being passed down it is the percentage of the varying degrees of a trait in a population. for instance gameness i believe has varying degrees from complete cur to dead game and everywhere inbetween. heredity takes into consideration genetics plus environment or nature vs nurture if you will. the problem with a lot of people is they believe that it has to be one or the other when in reality it is a combination of the two added together. an example is say a trait is moderately heritable which most behavioural traits are then selection for said trait will be successful as long as you breed for it and take into account environment. i say all this to say that if the inbreeding coefficient is skewed in one way or the other it can make a breeding look like an outcross when in reality it is line bred .
Heredity values are expressed from 0 to 1. 0 meaning no genes involved and only environment and 1 meaning 100 percent genetic involvement most behavioural traits fall in the moderately heritable range which is somewhere like 0.3 or 0.4. a trait being moderately heritable suggests that selecting for that trait will have an effect on the future stock.
Another interesting subject is estimated breeding values (ebv). there is an actual equation for both heredity and ebv but i doubt any scientist is willing to measure the traits of the APBT for us to find out. so the bet we can do with ebv is look at part of how they figure the equation out. basically when selecting a stud for let's just make this simple and choose on trait. i will choose gameness. ebv also explain the age old question of why curs produce gamedogs and why gamedogs produce curs. so here it goes when selecting the best stud to pass on gameness you want to look for a stud that first himself expresses the trait. this is the first step but not the only one. say for instance the stud possesses the trait you want and he has 4 other siblings and none of them carry this trait the mother and father don't carry the trait and the aunts and uncles don't either but the great great grandfather does. the dog in this scenario is not a good stud choice because clearly the genes for the trit you are looking for are not strong in this particular strain of let's say the eli line another scenario you could have is you happen to own a stud who does not carry the trait you want but you know that 3 out of his 4 siblings do his father does 4 of the mothers siblings do and both grandparents do. this dog is a much better candidate for breeding than the first dog. is he the ideal stud? no but still a better choice than the first dog. the best choice would be the same as the second dog accept this dog also carries the trait you are looking for.
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Originally Posted by EWO
