=&===w===x===y===z==={===|===}===~===

A B C D E F G A

W H W W H W W

The naturally occurring half steps between B-C and E-F fall in exactly the
right place to fit the scale formula, which means that the A natural minor
scale requires no sharps or flats in its construction.
Because natural minor scales are the basic diatonic scales of the minor
quality, they are considered minor keys and have their own key signatures,
just like major keys. Therefore, the key of A minor has a key signature of
no sharps and no flats. The rules for building other minor scales and key
signatures are the same as for major keys: from the tonic, write the letter
names of the notes in order, apply the interval formula, and adjust scale
tones up or down by means of sharps or flats as needed.

Relative Minor Keys
In the process of developing the natural minor scales and key signatures,
you may have noticed that the use of sharps and flats results in key
signatures that resemble those we have already seen. That is, the absence
of sharps or flats from the key signature of A minor makes it look like the
key signature of C major; E minor, with one sharp, looks like G major; and
D minor, with one flat, looks like F major. Major and minor keys that are
built on different tonic notes but share the same key signatures are
described as relative keys. For each major key, there is a relative minor,
and for each minor key, a relative major. To the eye, the key signatures of
relative keys are identical. Minor key signatures are laid out on the staff
just like major key signatures. The sharps and flats are in the same octave
and same order, which never varies. Only by analysing the melody to
locate the tonic can a key signature be identified as major or minor.

=&=¡============== E minor (relative to G major)

=&= ̈============= D minor (relative to F major)