  Uncertainties in stellar nucleosynthesis and their impact on models of
chemical evolution are discussed. Comparing the Type II supernova
nucleosynthesis prescriptions from Woosley & Weaver (1995) and Thielemann,
Nomoto, & Hashimoto (1996), it turns out that the latter predict higher Mg/Fe
ratios that are more favorable in reproducing the observed abundance features
of the Milky Way. Provided that chemical evolution models are calibrated on the
solar neighborhood, they offer a powerful tool to constrain structure
formation. In particular, galaxy formation models that yield star formation
histories significantly longer than 1 Gyr fail to reproduce the super-solar
Mg/Fe ratios observed in elliptical galaxies.
