Many use the terms "sexism" and "patriarchy" interchangeably. Against this imprecise usage, I'd propose the following definitions:
Patriarchy subordinates not only women but also younger men to the patriarch of an extended family, in a society where the relation of hierarchical dependency and obligation is the norm.
Sexism, in contrast to patriarchy, justifies subordination of women to men -- often rationalizing it as biologically or culturally grounded exception to the rule of independent individuals with equal rights -- but not younger men to older men, and it is found in a society where kinship has contracted greatly.
Clarified thus, these terms should help us grasp the North-South sexual gap. In the global South, patriarchy predominates; in the global North, sexism prevails.