The simple answer is mate choc to choc and you will get all choc. As I mentioned before, choc gene simply changes black to dark brown. It does not alter the plumage pattern. Thus, a solid black bird would be changed to a solid chocolate. A mottled bird becomes chocolate mottled. A laced bird would become chocolate laced. Since Seramas are not standardized for color by most breeders, you can get all sorts of color and pattern combinations. I had been working toward a flock of solid chocolates, and I strongly urge you to pick up where I left off. The main difficulty is lighter color in males' hackles.
For those who don't know, I had to sell off dozens and dozens of birds, including last year's hatchlings due to medical issues. I apologize for not having the energy to auction off and ship out so many birds. I know it would have been better for the breed to spread my stock out. My loss was Kdmp7244's gain! Now you will have to bug her for eggs and birds.
Choc is sex linked recessive. Unlike mammals, birds are reversed when it comes to sex chromosomes, as the female determines the gender of the offspring. Males are ZZ and females are ZW. The chocolate gene, designated choc, resides only on Z chromosomes. If the choc mutation gene is not present, the wild form of the gene, designated Choc+, is present. Choc+ is dominant to choc, so if Choc+ is present, the bird will NOT be chocolate. Males can be pure chocolate (choc/choc), chocolate carriers (Choc+/choc) which have black in their plumage unless other black modifying genes like blue, lavender or dun are present, or they can be pure 'not chocolate' (Choc+/Choc+). Females are called hemizygous because they can only have one copy of the sexlinked gene on their Z chromosome. The terms pure and carrier do not apply here. Females are either chocolate (choc/-) or not chocolate (Choc+/-).
Chocolate males have two copies of the choc gene. Black males can carry chocolate if they inherit one copy of the choc gene. Females can only have one copy of the chocolate gene, which will ALWAYS come from their father. If a female is black (or has ANY black in her feathers), she is not chocolate and her only gene at the choc location is Choc+ (i.e. "not chocolate").
So to summarize, here are the possible outcomes of matings:
Father X Mother = Sons & Daughters
choc/choc X choc/- = choc/choc & choc/-
(chocolate) (chocolate) (chocolate) (chocolate)
choc/choc X Choc+/- = Choc+/choc & choc/-
(chocolate) (black) (black choc carrier) (chocolate)
Choc+/choc X choc/- = Choc+/choc , choc/choc & Choc+/- , choc/-
(black choc carrier) (chocolate) (black choc carrier, chocolate) (black, chocolate)
Choc+/choc X Choc+/- = Choc+/Choc+ , Choc+/choc & Choc+/- , choc/-
(black choc carrier) (black) (black, black choc carrier) (black, chocolate)
Choc+/Choc+ X Choc+/- = Choc+/Choc+ & Choc+/-
(black) (black) (black) (black)