The Dorian and Mixolydian mode are very similar. Only the 3rd will tell them appart as you can see in the following chart:
Dorian:
Root-2nd-min3rd-4th-5th-maj6th-min7th
Mixolydian:
Root-2nd-maj3rd-4th-5th-maj6th-min7th
Because they are so close, we will be able to use both of these modes in the same context in most cases. Blending these two scales will give the listener a sense of rhythm flow because of the chromatic notes found when mixing them together.
In this lesson we'll use this principle on a G7 chord modulating on an A7 chord.
Memorize the scales, work on every lick, then make up your own!