Wikipedia
In societies that regard some races of people as dominant or superior and others as subordinate or inferior, hypodescent is the automatic assignment of children of a mixed union or mating between members of different socioeconomic groups or ethnic groups to the subordinate group. The opposite practice is hyperdescent, in which children are assigned to the race that is considered dominant or superior.
Parallel practices include patrilineality, matrilineality and cognatic descent, which assign race according to the father, mother, or some combination, without regard to the race of the other parent. These systems may not be mutually exclusive with hypo- and hyper-descent, since either parent (or both) might be of mixed race.
Attempts to limit (or eliminate) mixed-race populations by legal means are detailed in Anti-miscegenation laws and Anti-miscegenation laws in the United States