Chord sequence
A7 D7 A7 D7 A7 E7 D7 A7 E7
In every key
Four-note rootless voicings in their two forms, with the 3rd or the 7th on the bottom, played over the root.
Heard in A major
All the chords
The 12-bar blues in its simplest form, with dominant 7th chords on I, IV and V; the most commonly played progression in jazz.
Over A7 · V7/IV
Mode 5 of Major
Over D7 · IV7
Mode 4 of Melodic Minor
Over A7 · I7
Over E7 · V7