The Collaborative International Dictionary of English v.0.48:

Polygenic \Pol`y*gen"ic\ (-j[e^]n"[i^]k), a. (Biol.)
   Of or relating to polygeny; polygenetic.
   [1913 Webster]

WordNet (r) 3.0 (2006):

polygenic
    adj 1: of or relating to an inheritable character that is
           controlled by several genes at once; of or related to or
           determined by polygenes