I want to populate a drop down list based on check boxes/radio buttons value, help?

if you dropdown field is named "MyList", then this code will set the items in the dropdown to A,B,C

this.getField("MyList").setItems(["A","B","C"]);

Put a copy of this code in the mouse up for each radio button. Changing the Field name to the correct name, and each of the item lists to the items you want set by that radio button.

Using check boxes requires a more complicated strategy. Stick with Radio buttons if you can

You can delete and insert items. You can't show/hide items.

See Hiding and showing form fields using JavaScript by Thom Parker