Circadian Clock Gene Per2 Is Not Necessary for the Photoperiodic Response in Mice Ikegami, Keisuke ; Iigo, Masayuki ; Yoshimura, Takashi Abstract Publication: PLoS ONE Pub Date: March 2013 DOI: 10.1371/journal.pone.0058482 Bibcode: 2013PLoSO...858482I