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When marriage leads to inbreeding

In his letter of May 26, writer Mel Wolf questions why marriage between same-sex couples should be allowed while marriage between two siblings is not. The answer is, in a word, inbreeding. When two individuals with a common ancestor, i.e., a parent, reproduce, the probability of their children having congenital birth defects or a major disability skyrockets. This is also true of the offspring of two cousins, but to a lesser degree.

Close relatives such as these share a relatively greater amount of DNA, or genes, including those containing recessive traits associated with birth defects and mental disorders. Obviously, this would not be a problem in the case of two men or two women unless a sibling was to serve as a sperm or egg donor to produce a child — which no fertility specialist would permit.

Rita Zwern