Yes No check box

I'm new at php the form I'm creating has a Yes No checkbox my form works fine except if you check the Yes box and then check the No box they both stay highlighted. How can I make it so if the Yes box is checked and they check the No box the Yes box is unchecked. If you need my code let me know.

I've tried some of the code for checkbox but being new to php some of it doesn't make any sense.