Major 6ths on the Blues
Another common sound you'll hear applied in blues basslines is the use of the sixth.
The Sound of the Sixth
In most basslines the sixth has a melodic sound rather than a supportive sound. For example, you wouldn't want to emphasize the sixth on the first beat of a chord in your bassline. That would confuse the sound of the harmony. Instead, you'd want to use it as an auxiliary note to "melodicize" your chord tones. ("Melodicize" is my own made-up word. Use at your own risk!) Use your ear, listen, and judge what sounds right to you when creating your own basslines.
Major Sixth Chords
I haven't explained sixth chords yet, but you will run into them. So, here's a quick explanation:
A major 6th chord consists of a root, 3rd, 5th, and 6th. You can just think it’s a major triad with an added 6th. You will always find the 6th of a major 6th chord a whole-step (2 notes) above the 5th.
A major sixth chord is notated with the number 6 after the root note. For example, C6 or Eb6.
Using the Sixth
The sixth can often be used even if the chord symbol doesn’t indicate a 6th. You can almost always apply sixths on major triads. And, you can use it on dominant 7th chords often without trouble. Remember, you always have to listen to what you're playing and judge for yourself. You can't just apply something because you read it somewhere. There are many exceptions which take years of experience to understand.
The two blues basslines in the exercises should show you how you can fit a sixth in while still strongly outlining chord tones.
Don't forget to practice these lines and your own lines in different keys and at different tempos.