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Recent research has shown that, even though of course the number of genes involved in expression of a trait is not infinite, the general assumption that many genes with small effect are involved is very often is true. This is very convenient because this bell-shape fits the Normal Distribution. The normal distribution comes with a set of statistical rules that make it easier to make predictions. And that is what we want to do in animal breeding: predict genetic potential of animals and predict how the next generation will improve if we decide to use a certain proportion of the animals as parents. More on that in the chapter about ranking the animals.
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