Dominant Chord Forms, Extensions - NOT ALTERED
They can actually have every single chromatic note added to them, except for a major 7th. (The 7th has to remain flattened to keep the chord dominant)
I - IV - V (basic blues)
I - IV - I - IV - I - V - IV - I - V ("12-bar blues")
I - IV - I - IV - bVdim - I - VI - II - V - (I-VI-II-V) (Jazz Blues)
I - VI - II - V (Turn around at the end of Jazz Blues)
II - V - I (most important progression in Jazz, and the basic building block of most Jazz Standards)
Dominant ALTERED Chords
But there can also be 4 extensions added that are not in the C Mixolydian scale.
Those 4 extensions are: b5, #5, b9, and #9.
Adding any of these 4 notes to a dominant chord makes it "ALTERED".
Any combinations of those will also work. Each combination will add a different type of "spice" to the sound.
By using combinations of these 4 extensions, you will create extra tension during the 5 chord, creating higher "magnetism" of the 1 chord.