Now look at the scale tone chords derived from the A melodic minor scale. Because of the sharpened 6th degree, there will be more changes to the types of chords derived from this scale.
Notice that chord 2 is now minor instead of major, and also that chord 4 is major instead of minor and chord 6 is diminished instead of major. These changes are all brought about by the raising of the 6th degree of the scale from F to F#.
Scales and keys are only dealt with briefly here. For a detailed discussion of major and minor keys and scales, see Progressive Complete Learn to Play Rhythm Guitar Manual.