According to Gillman, "the novel's satire of racial classification by fractions of blood mirrors the problems in American race relations during both the antebellum period in which the novel is set and the 1890s when it was written" (87). America produced at this time the "pure white slave," much like Roxy and her child (Twain quoted in Gillman, 89).
For information on the one-drop rule, see the links section.