Chick color question

[chicksandchores]

I have a very mixed flock; the breeding age chooks are one RIR male, one BO male, three BSL hens, four BO hens, and five RIR hens. My last chick from a clutch of six hatched yesterday afternoon. I knew when I set that particular egg that it was a black sexlink egg but there’s no way of me knowing who the father was until adult feathers come in. From my understanding, a black sexlink comes from a cross between a RIR and a barred rock. My question for you genetics-buffs is, how did I get a black chick with yellow/orange legs and a white chest from either a buff Orpington-Black sexlink cross or a Rhode Island Red-Black sexlink cross? Is this typical? My entire breeding flock is hatchery quality, so I assume this probably has something to do with it?

 

[nicalandia]

I have a very mixed flock; the breeding age chooks are one RIR male, one BO male, three BSL hens, four BO hens, and five RIR hens. My last chick from a clutch of six hatched yesterday afternoon. I knew when I set that particular egg that it was a black sexlink egg but there’s no way of me knowing who the father was until adult feathers come in. From my understanding, a black sexlink comes from a cross between a RIR and a barred rock. My question for you genetics-buffs is, how did I get a black chick with yellow/orange legs and a white chest from either a buff Orpington-Black sexlink cross or a Rhode Island Red-Black sexlink cross? Is this typical? My entire breeding flock is hatchery quality, so I assume this probably has something to do with it?
View attachment 1741438

Its due to extended black e allele dominance. You see Extended black is dominant to all other e allele, the order of dominance is E > ER > e+ > eWh > eb, or Extended Black > Birchen > Wildtype > Wheaten > brown/partridge

The Black Sex links are the result of RIR which is wheaten, with Barred rocks which are Extended black, this cross results with black sex linked females that are E/eWh, so what ever you cross this hens with will have 50% chance of hatching Black down chicks(with yellow underside)