Watch the Harmonic Analysis online guitar lesson by Brad Carlton from Guitar Lab: The I7 bVII7 Progression

When dealing with unaltered dominant chords, there are two heptatonic scales which generate the various available harmonies. The Mixolydian mode, which is mode V of the major scale, and the Lydian b7, which is mode IV of the melodic minor scale. The formula for the Mixolydian is 1-2-3-4-5-6-b7 and the Lydian b7 formula is 1-2-3-#4-5-6-b7.