When discussing any genre of music, it's imperative to talk about how one form evolves into another. It's also important to keep in mind that many of these definitions are marketing tools to sell recordings or sheet music to certain demographics.

Blues emanated from field hollers which were close to African chants employing regional African modalities and scale patterns. These were incorporated into what we now know of as the blues.

Like folk (and as part of it) blues is a process, not just a genre. It's incorporated into later forms of jazz by Charlie Parker and Wes Montgomery who were thoroughly steeped in that tradition.