such as Leading tones, dissonance, resolution and the use of 7th chords.
Example: When using a I-IV-V chord progression, Say A-D-E, by adding the b7th note to the chord structure, you still have the Major triad notes, only adding the b7th to it. So, "A" Major has A-C#-E and A7 has
A-C#-E-G, which is still an "A" Major structure but becomes less stable from the added tension to the triad (think of it as a tripod with something added onto one of the legs, wanting to resolve and restablize). Certain notes bring more tension than others by dissonance and require a stronger resolution for stability. The b5th of the Blues scale (Blue Note) screams to be resolved as a harmonic interval and still sounds odd to me when used as a melodic interval.
When you study using the dominant seventh chord (a b7th note altering the Major scale that the parent chord derives from), your focus should change from the Major scale to a Mode because the Major scale has been altered. In this case, it would be the Mixolydian mode because it is the perfect match for the dominant 7th chord in Major Theory.
With regard to the topic of this thread, a hybrid scale was created that is extreamely popular and used by many Blues players. It was created by incorporating the Mixolydian mode and the Blues scale, which became known as the Mixo-Blues scale. It is the Mixolydian mode with a b3rd and a b5th added.
The Mixolydian mode intervals are; 1-2-3-4-5-6-b7
The Mixo-Blues scale intervals are; 1-2-b3-3-4-b5-5-6-b7