add example of line where father and mother mutation cols only contain one type of mutation

pyrat-data-2-mutations.csv

@@ -24,3 +24,5 @@ ID-022,Line-BC,12/12/2025,ID-F10,ID-M11,End of experiment,Mut-C,wt,Mut-B,het,,,M
 ID-023,Line-BC,18/12/2025,ID-F11,ID-M12,End of experiment,Mut-B,het,Mut-C,wt,,,Mut-B,het,,,,,Mut-C,het,,,,
 ID-024,Line-BC,01/12/2025,ID-F11,ID-M12,End of experiment,Mut-B,wt,Mut-C,het,,,Mut-C,het,,,,,Mut-B,het,,,,
 ID-025,Line-BC,01/12/2025,ID-F11,ID-M12,End of experiment,Mut-B,wt,Mut-C,het,,,Mut-C,het,,,,,Mut-B,het,,,,
+ID-026,Line-CD,01/12/2025,ID-F12,ID-M13,End of experiment,Mut-C,wt,Mut-D,het,,,Mut-C,het,,,,,Mut-D,het,,,,
+ID-027,Line-CD,01/12/2025,ID-F12,ID-M13,End of experiment,Mut-C,wt,Mut-D,het,,,Mut-C,het,,,,,Mut-D,het,,,,