There are other scales, such as the Dorian mode (1-2-b3-4-5-6-b7), but the minor pentatonic ... because the E7 features a G# note, the Major 7th in the key of A minor. Our A minor pentatonic ...

Harmonic minors use the relative major key signature and raise the seventh note of the scale. For example, in A harmonic minor there are no sharps or flats other than the raised seventh of G#.