  We examine the 2008-2016 gamma-ray and optical light curves of a number of
bright Fermi blazars. In a fraction of them, the periodograms show possible
evidence of quasi-periodicities related in the two bands. This coincidence
strengthens their physical meaning. Comparing with results from the periodicity
search of quasars, the presence of quasi-periodicities in blazars suggests that
the basic condition for its observability is related to the relativistic jet in
the observer direction, but the overall picture remains uncertain.
