How to load a combobox and reload another from my entity framework

Hi,
 
I have created a new entity framework.  After clicking finish, a new Model1.edmx was created on my project.
I have a form name material. This form as two comboboxs.
The first is named familia and the second sub-familia.
What I want is to populate the combobox familia with data from the table named familia. This needs to happen when the page is loaded.
Then, each time I click on the familia and choose one, the sub-familia combobox is loaded or reloaded with data that as a relation with that family.
The family table as the following fields:
 
FamilyID
FamilyName
CategoryID
obs - the familyname is the string that the user choud see in the combobox family.
 
The Sub-family table as the following fields:
 
SfamilyID
FamilyID (relational with the family table)
Sfamilyname< ...