Banana, Blueberry and Raspberry Muffins

While our family was in town we decided to head to Cannon Beach for the day. We stopped by a great little farmer's market while we were there and I found some plump and juicy raspberries and blueberries that I couldn't resist. I decided to make muffins with the last of the berries and a very ripe banana that needed to be used up. I used whole wheat flour and added low fat yogurt instead of