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In animal breeding a general assumption is that traits are determined by an infinite number of genes, each with a very small effect, so that the bell-shape is very smooth. It is also assumed that this infinite number of gene effects are all additive. The model underlying this assumption is called the infinitesimal model.
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DefinitionThe infinitesimal model assumes that all traits are determined by an infinite number of genes, each with an infinitely small effect. This assumption results in a smooth bell-shaped distribution that can be described by the Normal Distribution. This distribution comes with a number of rules that animal breeding theory is built on. |
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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