A natural minor uses A, B, C, D, E, F, and G. Its key signature has no sharps or flats. C major shares that signature, but A is the starting note and tonal reference here. The all-white-key description applies to natural minor; it does not describe every form of A minor.
A natural minor uses F and G in both directions. Harmonic minor raises G to G-sharp in both directions of this exercise. Classical melodic minor uses F-sharp and G-sharp ascending, then F and G descending.
Compare E-F-G-A, E-F-G-sharp-A, and E-F-sharp-G-sharp-A. Say which notes change before listening to or playing the next version.
The classical selector convention is not interchangeable with jazz melodic minor, which commonly keeps the raised sixth and seventh in both directions. Actual melodies can use minor inflections according to musical context.
On a narrow screen, scroll this table horizontally to read every column.