Tracking movement and gene expression of multiple flies using GFP and DsRED. Two male flies were placed in a vial and tracked simultaneously for 48 hours. Black/white bars indicate the light/dark cycle the flies were cultured under prior to the beginning of the experiment. Activity is expressed as distance moved per hour and fluorescence intensity is expressed as average pixel intensity per hour. 3xP3-GFP, transgenic strain I4, 7 days old (Green). Tet-on-DsRED, transgenic strain (2)26B, 1 month old (Red).