Melody and rhythm are almost inextricably linked. I say ‘almost’ because you can have melody or harmony without a distinguishable rhythm, and rhythm itself can exist with no melodic content at all.

You’ll find it in many old blues tunes ... 7 quality or implied tonality. So the basic underlying progression is F7 - D7 - G7 - C7. Figure 1 shows a rhythm part based on this progression ...