By adding one extra note (the flattened fifth degree) to the minor pentatonic scale, the Blues scale is created. This scale is used by all instrumentalists to create Blues melodies.
Like the minor pentatonic scale, the cross harp Blues scale can only be played on the low end of the harmonica. The G Blues scale is shown here along with a partial lower octave of the scale down as far as the 4th degree (C).
Here is a lick derived from the G Blues scale.
When improvising, it is common to use notes from all of the scales you have learnt. The following lick is made from a combination of the G mixolydian scale and the G Blues scale.