The story of the sex-linked Red gene originates from the breeding of Curiosity Julius, a Usual Abyssinian bred by Mrs Cathy Baker and owned by Mrs Muriel Fry (Zolda), with Mrs Wendy Chapman’s Wendele Whip Poor Whil, a blue tortie Burmese. (Although on ERoS she is described as Cream, she was exhibited as a kitten at the National Cat Club in 1981 described as Blue Cream Tortoiseshell and with this spelling of her name. Ref: Fur & Feather Volume 144 Number 4 535 page 46.) This line is now up to 10 generations and beyond, and carries through into several UK lines, as well as catteries in the United States and Switzerland.
The terms F1, F2 etc refer to how many generations a cat is away from the original outcross.