I guess u need to start redfining data tables first, u will need another table (tableEthinicity) where you can have Ethinc Category and Ethnic type 

then write a code something like ( i am saying like because I have not tested but should work)

Private Sub combo1_AfterUpdate()
   

    ETvalues = "SELECT [tableEthinicity].[ETID]," & " [tableEthinicity].[ECID]," & " [tableEthinicity].[ETname] " &"FROM tableEthinicity " & "WHERE [ECID] = " & combo1.Value
    Me.combo2.RowSource = ETvalues
    Me.combo2.Requery

End Sub