Cross breed one with breed two resulting in an F1. Breed the F1 back to desired breed let's say breed one. Then breed the resulting 3/4 1/4 calf back to an F1 cross of breed one and breed two. Hope this made sense.
breed brahman and angus and you get f1s.
take an f1 and breed it to an angus and you get a 1/4 brahman, 3/4 angus. take this animal and breed it to an f1 and you get 3/8 brahman, 5/8 angus. there are other ways too.
There are two ways to get to 3/8 - 5/8. Take Brangus ( I am looking at the IBBA brochure) The IBBA refers to the amount of Brahman Blood and the registered Angus and registered Brahman must be enrolled with the IBBA and all intermediate crosses are certified by the IBBA. Develop a 1/2 blood by breeding an enrolled Registered Angus to an enrolled Registered Brahman (F1). Also create a certified 1/4 blood by breeding a certified 1/2 blood to an enrolled Registered Angus. Then breed a Certified 1/2 blood (F1) to a Certified 1/4 blood to creat a registered Brangus (3/8 x 5/8 ) OR
Breed an enrolled registered Brahman to a Certified 1/2 blood (F1) creating a 3/4 blood. Then breed the 3/4 blood to an enrolled registered Angus.
After that just breed 3/8 x 5/8 to 3/8 x 5/8 for registered Brangus.
Brangus is the only American Breed that is produced from the registery of two pure bred breeds of cattle. The others use a "Breeding Up" program that creates "fullblood and purebred" cattle.