Combining 2 different recessive genes.
Example: Albino and Piebald
Albino x Piebald = all normals that are Het Albino and Het Piebald- considered Double Het Albino Piebald. You have to breed these double hets to each other to produce a snake that shows both Albino and Piebald traits at the same time- an Albino Piebald.
Double Het Albino Piebald x Double Het Albino Piebald will produce normals, albinos, and piebalds. Each egg has a 1 in 16 chance of producing an Albino Piebald.