ii-V can also be played without the 7th. One can play D F A D / G B D G instead of D F A C / G B D F. One can play in 4ths--D A / G D where D and A are called lower 5th and upper 5th respectively. Those notes are all lined up next each other on the circle--ii-vi-V-ii.

ii is a chord in its own right as is V. But are also part of another scale. D G C F, for example. D is ii and G is V of the scale of C major. Notice C is the next note in the sequence I listed. Like wise, you can look at G and C and the note to the right is F and so that is the scale that G and C are ii and V of. And so through all 24 arrangements.

Sometimes we play a pattern of the ii minor as 1 2 3 5 8 7 6 5. The 2 is called a "passing note." So using D G as an example, the pattern would be D E F A / G F E D. What the passing note tells us is what scale both D and G are ii and V of respectively. It will always be the major 3rd of that scale. In this case it is C since E is the major 3rd of C major.

If you look at a circle of 5ths, you'll that D and G are ii and V of C major. And E is the major 3rd. C, G and D are lined up in sequence clockwise while the passing note skips one more note over. The following circle of 5ths is wonderfully done and shows the relationships of the notes. You can turn the pointer to any note of the wheel and relationships hold true. I would copy this one if I were you. An excellent reference:

http://www.jmstaehli.com/images/music/Circle_of_Fifths.jpg

The following chart shows from left to right, the root, passing note, minor 3rd, major 3rd, 5th and 7th of all the possible chords in 12-TET. Look at the root D. It's passing note is E. Now look for E in the major 3rd column (4th one over from the left) and notice the root is C. The 5th of root D is A which is the passing note of the next note on the circle of 5ths after D going counterclockwise which is G. Notice the 5th of G is the root of the D scale.

C        D        Eb        E        G        Bb
C#        D#        E        E#        G#        B
Db        Eb        Fb        F        Ab        Cb
D        E        F        F#        A        C
D#        E#        F#        Fx        A#        C#
Eb        F        Gb        G        Bb        Db
E        F#        G        G#        B        D
F        G        Ab        A        C        Eb
F#        G#        A        A#        C#        E
Gb        Ab        Bbb        Bb        Db        Fb
G        A        Bb        B        D        F
G#        A#        B        B#        D#        F#
Ab        Bb        Cb        C        Eb        Gb
A        B        C        C#        E        G
Bb        C        Db        D        F        Ab
B        C#        D        D#        F#        A