On this thread, as per the category header and sticky, we use proper terminology, so I have no idea whether a "roo" is a marsupial or baby Kangaroo or what. In this thread, you have a cockerel, pullet, cock bird or hen.
With that out of the way, (and please take no offense) let's talk about your black Rocks. In some countries, the Black Rock is an accepted breed variety and honestly, I adore them personally. Do we need yet another Plymouth Rock variety in North America? No, quite honestly, as we cannot keep the Buffs, Columbians, and Silver Penciled up to snuff as it is. Too few keepers and quality breeders of these birds. Nonetheless, I love the Black Rock, especially if has the proper yellow shanks. Gorgeous birds, especially those I've seen from the UK.
Your K (cockerel) is a cross. He's not "pure" Barred Rock and is carrying only one barring gene, I would say. He's carrying a lot of black and his barring is very faint. He's a handsome, typey son-of-a-gun. The black pullet is a black Rock, but this is in phenotype, that which we "see". What she is in genotype, what she's carrying in genes underneath that we cannot see? Only through breeding her, if you wish to do so, will you know.
The top photo, showing the supposed parent stock shows "pure" BR females. But the male in that photo is standing back in the shadows, but with this unclear photo of him? I'd say he is too dark. He likely doesn't carry two barred genes. Thus, he only had a single pair to pass to his offspring, which explains why the pullet is a Black Rock and the cockerel is single gene cross.
What you need? You need a true bred male, if you wish to breed Barred Rocks. If you wish to breed Black Rocks, you could certainly push subsequent generations to the Black Rock by selecting only Blacks. Hope that helps.
Edited to add: What I know about the "science" of genetics wouldn't fill a thimble. But I know a couple of our semi-regular contributors are exceptionally well versed. Perhaps Joe Emenheiser will chime in. Joe knows this stuff cold.
