Representative wheel-running activity records of C57BL/6J, BALB/cJ, (BALB/cJ X C57BL6J)F1, and (BALB/cJ X C57BL6J)F2mice. Each record is for an individual mouse, double-plotted by convention so that a continuous 48 h are presented on each line, and each day's data is presented both beneath and to the right of that of the previous day. Times of activity are indicated by the vertical black marks. All animals were maintained on a 12 h light:12 h dark (LD) cycle for the first seven days shown, indicated by the bar above the record, followed by a transfer to continuous darkness (DD) begun at the usual lights-off time (17:00 Central standard time). (A) Female C57BL/6J; (B) male C57Bl/6J; (C) female BALB/cJ; (D) male BALB/cJ; (E) female F1; (F) male F1; (G) C57BL/6J-like F2; (H) BALB/cJ-like F2; (I,J) F2 mice with circadian behavior unlike C57BL/6J or BALB/cJ.
