The original Chocolate chimp in the UK was a female (Coco) that arrived at Twycross circa 1980's. The colour form was perpetuated by later breeding her with her grown-up son who also inherited the Chocolate gene from her. Twycross have produced a couple more since then also.
A normal black chimp, related to Coco and so carrying the chocolate gene, was later sent from Twycross to Colchester where it bred. Unknown to them it later mated with its grown offspring(also a carrier of the gene)and they produced another chocolate chimp. The full details are on a Colchester thread somewhere.
