Heat oven to 400 degrees F. Spray muffin tin with nonstick cooking spray.
In a large bowl, combine the flour, sugar, baking powder, and baking soda. Stir well until all ingredients are blended.
In another bowl, combine buttermilk, margarine, egg, and vanilla. Pour this mixture into the dry ingredients. Using a large spoon, gently stir ingredients just until moist (do not over-mix). Add fruit and stir gently (do not over-mix).
Spoon batter evenly into 9 muffin cups. Bake 20 to 25 minutes or until golden brown.