select combobox value and display releted combobox value

Question

hello everyone,
i am creating visual c# desktop application.
i have two table 1) Department Master
dept_id int primarykey,
dept_name varvhar(50).
another table is below:-
2) Contactperson Master
cont_id int primarykey,
dept_id int,
cont_name varchar(50).

now in windows form I put Two Different Combobox like, department combobox and contactperson combobox.
now when I select departmentname from department combobox then the releted data of contact person will show in contactpersonmaster.
pls help me.