$ cat pm_1079751_source2.gen 
C1, M1, 99999999, A, C, ... source2 info ...
C1, M2, 34787638, A, G, ... source2 info ...
C1, M4, 34787800, A, G, ... source2 info ...
C1, M3, 34787638, A, C, ... source2 info ...