Code:
Major Scale Box.
G|---2---|-------|---3---|---4---| 1st string
D|---6---|-------|---7---|---8---|
A|---3---|---4---|-------|---5---|
E|-------|---R---|-------|---2---|4th string
With bass guitar - Root on one and 5 on 3 is the basic, dirt simple, bass line used in Country. So what about 2 and 4? Well that's where the 3 & 7 go, i.e. that is where the flavor and color notes go.
R-5-R-5 just roots and fives as is R-5-8-5 are the back bone of classic ole time Country. But when you get into New Country then the 3 and 7 come on the 2 and 4.
4/4 time and a full Cmaj7 chord = R-3-5-7. Cm7 = R-b3-5-b7.
Is there more? Sure. http://www.jacmuse.com/form%20in%20music/2and4.htm
I'm sure you have already found/know this: http://en.wikipedia.org/wiki/Beat_(music)