12 Bar Blues is a pattern of chords which repeats every twelve bars. This progression is invaluable to the bass guitarists because of its use in many songs. For example, songs performed by Elvis Presley, Chuck Berry and the Beatles, such as "Hound Dog", "Johnny B. Goode" and " Roll Over Beethoven" are all based upon a 12 bar progression.
Example 15 uses a riff but is played further up the neck using no open strings at all. Memorize the finger pattern of this riff so that you can apply it to other positions on the fretboard for different chords.
Example 16 is the application of the previous riff to a 12 bar progression in A.
* Note: The D chord in bar 5 and 10 is played in different locations on the fretboard.