Alright I think I understand most of the genetics of Olive Eggers, but I think it's very simplified in most of the charts which indicate essentially *either* the parent of any given bird will pass on a blue (base blue) or a brown (base white, with brown overlay) gene in such a way that the brown is either "on" or "off" however in reality things are a little more complex than that. And in my experience blue is more complex than that too (a blue layer and a white layer don't just make chicks that lay *either* the same bright blue as a parent *or* plain white, the blue tends to dilute and become an in-between light blue color).
I'm interested in breeding for true breeding olive eggers out of original stock of crested cream legbars and black copper marans. This much I have down pat...
Year 1: BCM roo x CCL hens = F1 olive eggers that are sex linked due to barring of the CCL (males barred, females not) - 100% of eggs will be green (one blue base gene, one white base, brown overlay gene)
Year 2: Breeding F1 hens back to BCM roo = Olive egger back-cross (let's call them "spinach eggers" for clarity) which are not sex linked (all solid, no barring) - 50% of eggs will be darker green than F1 (one blue base brown overlay gene, one white base brown overlay gene - is that right???), 50% of eggs will be brown (white base, brown overlay). The brown egg layers will be culled from the project.
This is where things get a little iffy to me. Let's say I like that second generation back-gross "Spinach eggers" Where do I go from here to work towards stabilizing the line for true breeding?
Just spitballing here...
Year 3: Spinach egger crossed to F1 olive egger roo.. I can't cross two "spinach eggers" because I won't know if the roo would have the genetics of a brown egg layer or a green egg layer. Since the spinach egger hen is solid and the F1 olive egger roo is barred, half the chicks would be barred (no sex link)
F1 roo would pass on *some brown* presumably right? And may or may not pass on a blue vs white gene (50% chance)
Spinach egger hen would pass on *some brown* for the same reason, and either a blue vs. white gene (50% chance)
25% of chicks would get the double blue, and some brown, 50% would get the single blue and some brown, and 25% would get no blue and be culled from the project.
Again, I wouldn't know if any given roo is in that 25% so I couldn't retain any of the roos from this generation for breeding.
Year 4 and on: Start selecting eggs for the best color (most blue and most brown for darkest green) and cross back to the F1 olive egger roo. Though the olive egger roo may or may not pass on blue, all of the hens would have blue and therefore all offspring from gen 4 onward would lay some shade of green egg. I suppose there's a very very small chance of a recessive white cropping up in the hen combining with the recessive white in the roo but if I'm selecting the most pigmented (blue/brown, very green) eggs to hatch and breed back, the likelihood of that happening declines with each generation.
If I wanted sex-linked chicks again, I would have to go back to the last generation of all solid offspring to get a solid roo - that would be Spinach eggers. I could cross those with my current generation of best barred green egg layer hens. I can reasonably assume the hens will pass on a blue gene with brown overlay. The roo will pass on some brown, and either a white or blue gene to produce sex linked chicks that will lay either a nice dark green, or a slightly more khacki (less blue) green egg layer. All the females will be solid and the males will be barred. Since the females are solid I would not be able to cross the next generation for more sex links. It would always have to be a cross between the barred females in the line I'm selecting for greenest eggs, back to the solid spinach egger roo.
Is this math right? Geneticists? Please
You’re right about the sex-linking, but only half of the chicks would be barred in the above instances, since the rooster would only have one copy of the barring gene.