G/D as a function of metallicity for the 2 values of X_CO: X_CO,MW (left) and X_CO,Z (right) with the chemical evolution model of Galliano et al. (2008). The colours and symbols are the same as for Fig.4. The dark grey stripes show the range of values from the Galliano et al. (2008) chemical evolution model. The black dashed line represents the reference scaling of the G/D with metallicity (not fit to the data). The black dotted and dash-dotted lines represent the best power-law and best broken power-law fits to the data.