All major keys have a relative minor. To find the relative minor, just count down three semitones from the tonic of the major scale. For example, the relative minor of C major is A minor.

Harmonic minor scales use the relative major key signature and raise the 7th note of the scale (e.g., in A harmonic minor there are no sharps or flats other than the raised 7th of G♯). Melodic minor scales use the harmonic version ascending and adhere to the relative major key signature on the way back down.