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title: "6.13 Rate of inbreeding and active population size"
canonical: "https://wiki.groenkennisnet.nl/space/TAB/288719190/6.13%20Rate%20of%20inbreeding%20and%20active%20population%20size"
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The rate of inbreeding depends on the population size. It is important to realise that this refers to the *active breeding population*, and not the total population size. To be able to predict the rate of inbreeding to the next generation, you need to know how many males and how many females participate in breeding.  In figure 10 you see the relationship between population size and rate of inbreeding in a balanced breeding population, which means equal numbers of breeding males and females. The rate of inbreeding increases very rapidly with decreasing population size, when population size drops below 50. So when 25 males and 25 females are used as parents for the next generation, and they are mated at random.

![image](media://cce7e4e2-2b7f-41b3-8d49-ea54eadc7e73)

The fact that the animals are mated at random is quite essential here. Because non-random mating can influence the rate of inbreeding. After all, an animal is inbred if, and only if, its parents are related. So to avoid inbreeding, you can try to mate unrelated animals. This works, but is only a temporary solution. Eventually all animals are related again and mating related animals can’t be avoided anymore. The rate of inbreeding will become the same as when random mating would be applied. The consequences of inbreeding are postponed, not avoided. This is illustrated in figure 11b.

** Figure 11. **Figure 11a illustrates the increase in inbreeding across generations when random mating is applied. In figure 11b the effect of avoiding mating related animals is indicated. The inbreeding level drops immediately, but slowly approaches the situation under random mating again. In figure 11c the increase in inbreeding due to mating of related animals on purpose is illustrated. This effect can be reversed by returning to random mating again.

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