Close marriage

Close relatives (or kinship) are defined as having common ancestors within 3 generations. If they are intermarried, it is called a close marriage. Closely married couples may have the same gene from their common ancestor and pass it on to their children. If the gene is inherited in an autosomal recessive manner, its children may develop disease because they are homozygous for the mutation. Therefore, intimate marriages increase the risk of certain autosomal recessive diseases. The probability that a marriage between close relatives results in such a pair of homozygous or identical genes in the children is called the inbreeding coefficient (IF).