Exogamy, sometimes defined as out-marriage, is a tradition that forbids unions between members of other groups. In certain areas, the exogamy laws may even stipulate which outsider group a person must married into.
For example, an individual of Jewish origin may also wed outside of their ethnic endogamy in order to reduce the risk that their children would contract Tay-Sachs disease. In a same vein, someone else of African origin may wed outside of their race in order to reduce the likelihood that their offspring may get severe cellular anemia.