Hertzsprung–Russell diagram of a 1.0 M_⊙ model at solar metallicity (top left panel). Also shown are the evolution of ¹²C/¹³C (top right panel), [C/O] (bottom left panel), and [N/O] (bottom right panel) for the 1.0 M_⊙ and 1.5 M_⊙ model at solar metallicity (blue and purple lines, respectively) and for 1.0 M_⊙ at [Fe/H] = –0.54 (orange line) from the subgiant branch to the RGB tip and later from the core He-burning to AGB phase. The tracks show the predicted behaviour from stellar evolution models taking into account or not the effects of thermohaline mixing (solid and dashed lines, respectively). The position of the beginning of the first dredge-up, the RGB bump, and the core He-burning phase are indicated in each panel (triangle, star, and square, respectively).