Preheat oven to 375 degrees F (190 degrees C). Grease muffin cups or line with paper liners.
In a large bowl, mix together cornmeal, flour, sugar, baking powder, baking soda and salt. In a separate bowl, beat together egg, buttermilk and oil. Stir the wet ingredients into the dry ingredients just until moistened.
Fold in jalapeno peppers. Fill muffin cups right to the top, and bake for 18 to 20 minutes in the preheated oven.