" Based on scientfic facts that a animals bite force is impacted and contributed by the animals jaw stucture, jaw muscles, and weight.
but how can this be if there bite force in 100% genetic. "

The bite force of a animal is determined by body size, weight and jaw size amongst other things to be able to put a accurate number down for the bite force of the test subject. This does not mean that size, weight and jaw size determine if a dog can bite hard or not. Also, you can train and condition for a hard bite, there is still no way of making the dog bite harder than it wants too. ( some dogs don't try to break bones everytime they bite a hog) I do believe in working the mouth just like any other muscle to prepare him for his job.