Dropdownlist to be created Dynamically

Hi Friends,
i have a Button control outside of my gridview Control on web page.i want to Add new Rows in my Gridview on button click event of the (Button)control.
1)how can i add the new rows inside of a Gridview on Button click event.
2)The row also contains Dropdownlist control which is going to be filled from Database table.
how can i met the above 2 requirements.
 
Pl Reply,
 
regards,
aamir