Evolutionary tracks of mass donors (panels a–d) and of mass gainers (panels e and f) for selected binary models in the Hertzsprung-Russell diagram. The tracks are labeled with the selected initial stellar masses. The mass gainers shown in panels e and f are the counterparts to the mass donors shown in panels a and b, respectively. The panels a–c depict the donor evolution for three different initial orbital periods, for binaries with a fixed initial mass ratio of q_i = 0.7. Panels b and d: donors for the same orbital period (P_i = 40 d) but for two different initial mass ratios. In the panel a diagram, arrows identify different parts of the same tracks. The tracks and star symbols are color-coded as in Fig. 1. Double rings marks a predicted merger situation; our calculations end there.