I believe that Darnell is indeed Earl Jr.'s father, and that the DNA test did not pick it up because of something that the FBI did to Darnell during the time they were in the witness protection program. Remember, they said they were changing his blood type?
No one knows.....in the last episode it was found out that Earl wasn't Dadge's dad but Lil Chubby was. And then after Earl says that, Darnell barges in and says that Earl Jr. isn't his child either....then Joy says "Now lets just all calm down." then is says 'to be continued'. So no one really knows for sure....besides Dodge and Earl Jr. are about the same age and Darnell didn't meet Joy until, before her and Earl got a divorce.
From creator Greg Garcia "We never really got the chance to fully figure it out but the talk in the writers room was that Earl Jr’s Dad was going to be someone famous. Like Dave Chappelle or Lil John. Someone that came to town on tour and Joy slept with. But when we got canceled we never got the chance to figure it out. I was worried about doing a cliffhanger but I asked NBC if it was safe to do one at the end of the season and they told me it was. I guess it wasn’t.
crabman is earl jr father the toothbrushes used to verify dna were the same ones from when earl lived there only verifying earl is not the father of earl junior but is dodges father. crabman having his blood type changed and his chemical make up or dna are completely different things
According to Greg Garcia, the show's creator the writers never really concluded who Earl Jr.'s dad would be. They discussed the possibility that it would be someone famous like Dave Chappelle or Lil John. Someone who came thru town on tour that Joy slept with. Unfortunately NBC gave the green light to end on a cliffhanger and then proceeded to cancel the show. I guess we'll never know.