Throughout history and across countries, women appear more likely than men to enter politics on the heels of a close family relative or spouse. To explain this dynastic bias in women's representation, we introduce a theory that integrates political selection decisions with informational inequalities across social groups. Candidates with dynastic ties benefit from the established reputations of their predecessors, but these signals of quality are more important to political newcomers such as women. Legislator-level data from twelve democracies and candidate-level data from Ireland and Sweden support the idea that dynastic ties are differentially more helpful to women, and that the quality of predecessors may be more relevant for the entry and evaluation of female successors than their male counterparts. The role of informational inequalities is also reflected in the declining dynastic bias over time (as more women enter politics), and in the differential effect of a gender quota across Swedish municipalities.