The correct answer is hypodescent.
When it comes to the Susie Phipps case, she was denied her rights because she had one black ancestor. Hypodescent means that a person is assigned to a particular group (in this case, the 'subordinate' race) based on their skin color - hypo means 'below,' so these people are classified as being inferior to the hyper group. Susie identified herself as a white person (and she was overwhelmingly white), however, due to the fact that her great grandmother was black, she was still denied equal rights as white people.