Mixolydian, the 5th mode.
The mixolydian mode fits when played over 7th chords, because the only difference between it, and the major scale is that the 7th note is lowered a half step.
The musical term for the lowered 7th note is called dominant.
Here is how this scale looks based on the tone, semi-tone method.
This is E Mixo, so because it's the 5th mode, we are in the key of A, watch the key signature.
This scale is not used to much in jazz, but it can be useful in pop music as there are a lot of dominant chords.
Below is a list of some dominant chords from another lesson on walking bass lines.
This mode will work well when playing over any off these chords but for the F7 chord, you need to start on F, for the D7 chord you must start on D... and so on.
Don't understand the fingering chart? Go to the bass guitar scales intro.
And here is the fingering, (starting with open E)...