The original Cuckoo Orpington LF was bred and introduced by William Cook’s daughter Elizabeth Jane in 1907 not many years after his death.
Apart from the standard Cuckoo colour all solid colours can be created in a cuckoo variety .
THE BARRING IN THE CHOCOLATE CUCKOO IS A SEX LINKED DOMINANT GENE
In poultry the sex of any chick is determined by the hen not the cockerel. The cockerel carries two Z chromosomes so he is ZZ. The hen carries one Z chromosome and one W chromosome so she is ZW.The cockerel must pass one of his Z chromosomes onto his offspring so any sex linked genes that are on that chromosome such as Silver, Bantam, Barring and Chocolate will be inherited. The hen can pass either her Z or her W chromosome on to her offspring. If she passes her Z chromosome on her chicks will be male and they will inherit all the sex linked genes that are on that Z chromosome but if she passes her W chromosome on, her chicks will be female and they will inherit none of the sex linked genes she is carrying. Genes that are sex linked can only be carried on the male chromosome.
THE CHOCOLATE IN THE CHOCOLATE CUCKOO ORPINGTON IS A SEX LINKED RECESSIVE GENE
So a cockerel needs two copies of the gene to be chocolate but the hen only needs one.
Chocolate x Chocolate = 100% Chocolate
Black split Chocolate cockeral x Black hen = 25% Black split cockerals/ 25% Black cockerals/ 25% Black hens/ 25% Chocolate hens
Chocolate cockeral x Black hen = 50% Black split cockerals / 50% Chocolate hens
Black cockeral x Chocolate hen = 50% Black split cockerals/ 50% Black hens
Black split Chocolate cockeral x Chocolate hen =25% Black split Chocolate cockerals/ 25% Chocolate cockerals/ 25% Black hens/ 25% Chocolate hens