Hmm.. If i understand what you are asking. It's not as simple as that really. In a Scale, certain chords will be minor, major and diminished...
An example of the C scale..
With C major being your key, you would usually play a C, Am, F, G.. Not in that order, but those are the chords that go well with any song in C major (Goodbye my lover - James Blunt, Superman - five for fighting.. etc)
Now how that works is this.. in a C major you get C D E F G A B C
And that works out to be:
Cmaj
Dmin
Emin
Fmaj
Gmaj
Amin
Bdim
Cmaj
So.. In saying that.. Am is the relative minor of a C major.. So if you were playing in Am, you would actually be playing in C major because its the same key.
http://korsmo-tech.com/Circle%20of%20Fifths%20wheel.gif
That shows you the minor's relationship to the major..
Not sure if i actually answered your question or not! ???