Combine sugar and water in a small saucepan, and bring to a boil. Cook for 1 minute over medium heat, stirring until the sugar dissolves. Combine the sugar syrup, blackberries, raspberries, and lemon juice in a blender. Pulse 3 times or until the berries are chopped. Cover and chill.
Note: Store remaining sauce in an airtight container in refrigerator. Serve over low-fat ice cream or pancakes.