How can we explain the fact that the incidence of hereditary diseases in small, isolated communities is much higher than usual?

1) Family marriages are common in small communities.
2) Family marriages lead to an increase in the homozygosity of people for a number of reasons.
3) The transition of recessive mutations to a homozygous state leads to various diseases that, as a rule, do not appear in a heterozygous state in populations where related marriages are not accepted.

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