listbox of combobox2 depends on value choosen from listbox of combobox1

I have a userform contain two comboboxes , one for names and second for marks, the RowSource of combobox Names is column A , the RowSource of Combobox Marks is second row from column B to M.
I want a code in commandbutton1: if I choose the name from combobox Names like George , I want List of combobox Marks show just the head column where marks exist ( Mark A, Mark C , and Mark G for George names and Mark B , Mark D ,Mark J forg Elie names ) , and if I choose name doesn't have any Marks like Helen or Philip I want combobox Marks show all Marks names in second Row ( from Mark A , Mark B … till Mark L)

see attached file

Thanks in advanced