Because, close relatives (or kinship) refers to the ancestors who share the same * * * within three generations. If they get married, it is called consanguineous marriage. Couples who are closely related may get the same genes from their ancestors and pass them on to their children. If this gene is autosomal recessive, its children may get sick because they are homozygotes of the mutation. So inbreeding will increase the risk of some autosomal recessive genetic diseases. Inbreeding coefficient (IF) is called inbreeding coefficient, which increases the probability that children will get such a pair of homozygous or identical genes.