Simulations of the chemical evolution of local group dwarf galaxies are presented, which incorporate Type II and Ia supernova feedback and monitor isotopes up to Pb. I discuss the influence of ram-pressure stripping and SNe feedback on the different chemical and gas properties of dwarf spheroidals and irregulars. Peculiar trends of s-elements suggest a strong contribution from low and intermediate-mass stars. This places a lower limit on the duration of star formation in dwarf spheroidals, which has cosmological implications with regard to the dark matter content of dwarfs and the epoch of reionization. The role of dwarf galaxies in polluting the high-redshift universe with metals is investigated by comparing chemical properties in the ionized winds and neutral ISM of dwarf galaxies with IGM and DLA data.