Radio button limits selectable check boxes

Hi all,
 
I am creating a pdf form and I need some JavaScript to control the amount of selectable check boxes in a group.
 
The structure is as follows:
 
If the radio button 'yes' is selected, then the user can select a maximum of 2 check boxes from a total of 12.
If the radio button 'no' is selected, then the user can only select 1 check box from a total of 12.
 
Does anyone know how I can achieve this?
 
Thanks!