Variable stars as tracers of stellar populations in Local Group galaxies: Leo I and NGC 6822

Results are presented of a study of the variable starpopulations in the dwarf spheroidal galaxy LeoI and in the dwarf irregular galaxyNGC 6822, based on time series photometry obtained with the Wide Field Imager of the 2.2 m ESO/MPI telescope ( LeoI) and the Very Large Telescope(NGC 6822). We found about 250 (lower limit) variables in LeoI most of which are RR Lyrae stars. In NGC 6822 we identified 450 candidate variables among which about 20 are RR Lyrae stars, and many are low-luminosity, small-amplitude Cepheids.