The Collaborative International Dictionary of English v.0.48:

Prepotency \Pre*po"ten*cy\, n. [L. praepotentia: cf. F.
   pr['e]potence.]
   [1913 Webster]
   1. The quality or condition of being prepotent; predominance.
      [Obs.] --Sir T. Browne.
      [1913 Webster]

   2. (Biol.) The capacity, on the part of one of the parents,
      as compared with the other, to transmit more than his or
      her own share of characteristics to their offspring.
      [1913 Webster]

WordNet (r) 3.0 (2006):

prepotency
    n 1: the state of being predominant over others [syn:
         predominance, predomination, prepotency]