The Tonkinese owes its characteristic coat-pattern to the incomplete dominance of the genes which produce the 'solid' coat-pattern of the Burmese (cb), and 'pointed' coat-pattern of the Siamese (cs). Therefore, all progeny resulting from a mating of a Burmese with a Siamese will be Tonkinese and will have the typical Tonkinese coat-pattern (cbcs), but at this stage they may not necessarily have the desired type, eye colour or clarity of coat-pattern.

Mating Tonkinese with Tonkinese consistently produces 3 variations of the coat-pattern (with the associated eye-colour) resulting from the cb and cs pairing:

1. The intermediate Tonkinese coat-pattern, referred to in the USA as the 'mink' pattern (cbcs), with the bluish-green eye colour

2. The 'solid' variant coat-pattern (cb), with green/yellow eye-colour.

3. The 'pointed' variant coat-pattern (cs), with clear blue eye-colour.

Irrespective of coat-pattern, the progeny of a Tonkinese x Tonkinese mating are Tonkinese and should be registered as such. The 'solid' pattern should not be used in a Burmese breed programme; the 'pointed' pattern should not be used in a Siamese breed programme.

A Tonkinese variant may not be eligible to be shown under the GCCF, because there is no provision for Any Other Variety Open Classes, but if it has excellent "Tonkinese type" it would be a valuable contributor when used as part of the Tonkinese breeding programme. Furthermore, a 'solid' Tonkinese variant (cb) mated with a 'pointed' Tonkinese variant (cs) can only produce the Tonkinese coat pattern (cbcs). Over several litters, the expected ratio of coat-patterns produced by a Tonkinese x Tonkinese mating will be 50% Tonkinese (cbcs), 25% 'solid' (cb) and 25% 'pointed' (cs). From a Tonkinese variant x Tonkinese mating, the expected ratio of coat-patterns (over several litters) will be 50% Tonkinese coat-pattern and 50% variant coat-pattern according to the type of variant used, i.e. 'solid' or 'pointed'

Mating Tonkinese with either a Burmese, or a Siamese, is likely to cause divergence of the "Tonkinese type" and is not recommended. Therefore, since 1st January 1997, all progeny from back-cross matings (i.e. the mating of a Tonkinese, or Tonkinese Variant, with a Burmese or Siamese) are placed on the GCCF Reference Register.

It is necessary to permit the breeding of first generation Tonkinese (Burmese x Siamese) until such time as the Tonkinese gene pool is considered to be large enough, and diverse enough, to restrict it to Tonkinese only. However, in order to perpetuate the Tonkinese breed as such, it is required that Tonkinese be bred with Tonkinese. Therefore, since 1st January 1999, all progeny from first-cross matings (i.e. the mating of a Burmese with a Siamese) are placed on the GCCF Reference Register.

1. Cats selected for use in breeding programmes should be healthy and free from any known deleterious alleles or veterinary defects.

2. Tonkinese selected for showing and breeding should be as near the desired type as possible, having clearly defined Tonkinese coat-patterns and bluish/green or greenish/blue eye colour.

3. Tonkinese variants selected for use in the breeding programmes should be as near the desired Tonkinese type as possible and preferably have come from lines with the potential to produce excellent Tonkinese coat-pattern and eye-colour.

4. Burmese and Siamese, to be used in the breeding of first generation Tonkinese should be good examples of their breed and should have only Burmese or Siamese, respectively, in their pedigrees.

It is not acceptable to include Burmese-cross breeds (e.g. Bombay or Asian) or Siamese-cross breeds (e.g. Oriental or Balinese) in the Tonkinese breeding policy because such breeds will introduce genes that are alien to the Tonkinese genotype.