Fig 3. (i) The number of fragments X_tot and Y_tot of dividing cells and (ii) the number of X-dominant and Y-dominant cells at corresponding time for the transfer constants (A) D = 0 (B) D = 0.001 (C) D = 0.01 and (D) D = 0.02.

Initially, the numbers of X_tot and Y_tot are approximately equal and, as time goes on, cells are differentiated into either of X-dominant or Y-dominant compositions. For D = 0 (A), the system is unstable: only X-dominant cells (for this run) dominate (ii) and finally, cells cannot continue growth. For D = 0.001 (B) and 0.01 (C), the system is stable; X and Y fragments coexist in each cell with unequal population (i). Here, the asymmetry between the major and minor fragments gets smaller as D increases. In addition, the two types of cells, X-dominant and Y-dominant cells coexist with the equal population (ii). As D increases further [D = 0.02 (D)], the system gets unstable and only either of X or Y remains (ii). The parameters are V_Div = 1000, N_cell = 100, k^f = k^b = 1, and k_x = k_y = 1.