Cinnamon is a sex-linked recessive gene, this mutation is responsible for the brown phenotype throughout the plumage of Cockatiels, the reason for this is that this gene inhibits the final stage of melanin production resulting in birds not being able to produce shades of black and grey pigments rather leaving them shades of brown, this mutation effects the plumage as well as soft-tissue.
This mutation was established in Belgium in 1968 and is currently widely available around the world.
This mutation combines well with Lutino, Pearl, Sex-Linked Yellow Cheek, Recessive-Pied as well as all different kinds of psittacin reducing/changing mutations.
It is considered undesirable to pair Cinnamon to melanin altering mutations such as Dominant Silver, Emerald and Olive as a combination of these mutations would be impossible to identify on a cinnamon phenotype without test breeding.
Cross breeding Cinnamon to Bronze Fallow could also cause confusion as visual Cinnamon Bronze Fallow birds would look Cinnamon Lutino and could leave breeders unhappy with the results.