I do have White Jersey Giant hens in this separated flock also. I just don't know which eggs are from the Delaware's or the Jerseys as they all use the same nest boxes. I believe all the hens are laying as I have 8 Delaware and 6 Jerseys and I'm getting 10 eggs on one day and 12 the next. Not the best of control I realize, there again it's a space issue.Yes, genetics can be complicated!
Some points about barring:
--it can appear in both males and females (example: Barred Rocks)
--barring is a dominant gene, so you can see if it is present in a black chicken (example: Barred Rocks have barring, Black Jersey Giants do not).
--white barring on a white chicken is not obvious.
--Because barring is on the Z sex chromosome, a cross of barred and not-barred will give different results depending on which one is the father and which is the mother.
--A hen gives a Z chromosome to her sons and a W chromosome to her daughters. That means she can give barring to her sons but not to her daughters. Mating a barred hen with a not-barred rooster produces sexlink chicks. (Examples: Rhode Island Red rooster with Barred Rock hen, or solid black rooster with Delaware hen. Either cross will produce black sons with white barring, and black daughters with no barring.)
--a rooster has two Z chromosomes, so he can have either one barring gene or two. He gives one chromosome to each chick he sires. If he has two barring genes (one on each Z chromosome), then he gives one to every chick, males and females alike. If he has one barring gene and one not-barring gene, he gives barring to half of his chicks and not-barring to the other half, but again it has nothing to do with which ones are males vs. females. In either case, you cannot sex the chicks by looking for barring.
Since your chicks are black with barring, we know the White Rock is not giving genes to make them white all over. We do not know if he is giving genes for just black (in which case they got barring from a Delaware mother and are males), or if the rooster is giving genes for black and for white barring (in which case the chicks could have either mother, and could be males or females.)