The exact location of the gamma-ray emitting region in blazars is still controversially discussed. Different theoretical models suggest either small (~ 100-1000 Schwarzschild radii) distances from the supermassive black hole near the jet base, or larger distances, at the radio shocks on pc scales. In order to attack this problem we present a detailed study of the relation between cm to mm radio and gamma-ray variability/ flares in the light curves of a large sample of Fermi-bright blazars. The long-term cm to short-mm radio data of 56 sources obtained by the F-GAMMA program at 10 frequency bands are combined with Fermi LAT gamma-ray lightcurves covering a total period of 3.7 years.
A sophisticated statistical cross-band and stacking analysis is presented together with more direct analysis of lightcurve properties, such as relative timing and onsets of radio/gamma-ray events. Our results reveal for the first time highly significant correlations with time delays strongly decreasing towards the short-mm bands indicating co-spatial emitting regions in the shocks on pc scales. Significant differences between FSRQs and BL Lacs are presented and possible correlations with other source parameters (e.g. blackhole mass) are discussed.