As explained above the Burmese breed in the UK is descended from one original cat, Wong Mau, she and her immediate descendents were out-crossed to a number of Siamese, (ten individual Siamese can be identified within the recorded breeding programme followed in the USA during the 1930s and „40s) and supplemented by probably two additional Burmese hybrid (Thong Deang) imports. The Burmese cat gene-pool imported into the UK between 1949 and 1970 was based on these thirteen cats. The development of the red, cream and tortie colours broadened the gene-pool further with the introduction of a further three out-crosses to the breeding programme; years later another, a British Red Tabby called Cornish Treacle, was mated to a Burmese and one of his descendant appears in Burmese pedigrees.
This gives a total current gene-pool based on 17 or so individual cats. This is a very small genetic basis for a pedigree breed, one of the most limited of any recognised breed of pedigree cat in the UK. It is something breeders must pay particular regard to in continuing the breed into the future, especially as the gene-pool in the UK has been closed since 1992 which means no imported Burmese can be registered with GCCF and used in the breeding programme and no outcrosses to other breeds have been permitted, for registration within the terms of the Burmese Registration Policy, for some forty years (Burmese out-crossed to Asians are permitted within the Asian Registration Policy, and similarly for the Devon Rex).
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| Burmese Cat |
1. Agouti (A) - the natural “wild” gene that is the basis of the tabby cat. The base agouti pattern is bands of black on a yellow background; in the cat this is overlaid with one of the tabby patterns. The Burmese is a non-agouti breed, however, it is important to understand that all cats have an underlying tabby pattern; this can sometimes be seen as faint tabby markings particularly on the legs, tail and face on “self-coloured” cats.
2. Ticked (T) – one of the four tabby patterns, this is caused by an incompletely dominant gene which removes most of the stripe pattern leaving the ticked agouti base pattern on the body with minimal overlaying stripes on legs, chest (necklace) and face. Selective breeding of Burmese to eliminate any evidence of ghost tabby markings has in effect selected for Ticked Tabby based cats (as opposed to Mackerel or Classic tabby based cats which frequently show some ghost barring particularly in red and cream coloured cats). Thus it is likely that vast majority of Burmese cats are Ticked Tabby based.
3. Non- agouti or “hypermelanistic” (a) - a recessive gene mutation that turns the original “wild” tabby cat into a self black by overlaying the agouti base colour with melanic pigment, making the whole animal appear black, although often in certain light the underlying tabby pattern may still just be discernible. Other genes work to change this black pigment to other colours (see below).
4. Burmese Colour Restriction (cb) - a mutation on the albino allele one step up from the Siamese (Himalayan) gene (Cs). This reduces the amount of pigment produced in the coat but, because it is thermo-sensitive, the pigment is darker at the points, where the skin is cooler and (slightly) lighter on the body which the skin temperature is warmer; the action of the Burmese gene causing a genetically black cat to turn sepia brown, a red cat to turn pale tangerine. The Burmese Colour Restriction gene is incompletely dominant over the Himalayan gene at the same locus on the chromosome with the result that the inheritance of one Burmese gene and one Himalayan gene results in colour restriction mid-way between the two, i.e. what we now recognise as Tonkinese Colour Restriction (cbcs). Wong Mau was of Tonkinese colour restriction as she had one of each of these genes.
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| Burmese Cat |
6. Orange (O) – this is a mutation on the X chromosome and is thus sex-linked. The gene eliminates all melanin pigment (black and brown) from the hair fibres, replacing it with phaenomelanin, a lighter compound appearing yellow or orange depending on the density of pigment granules. The O allele is also epistatic over the non agouti genotype; that is, the agouti to non-agouti mutation does not have a discernible effect on red or cream coloured cats, resulting in these self-coloured cats displaying tabby striping independent of their genotype at this locus. This explains why you can usually see some tabby pattern on red and cream coloured Burmese cats, even if only on the head/face and often as ticking on the body. Rufus polygenes, as yet unidentified, affect the richness of the orange gene‟s expression.
7. Dilute (D) – a recessive gene which reduces and spreads out the pigment granules along the hair-shaft and turns a seal brown to blue, chocolate to lilac, and red to cream.
Dilute Modifier (DM) – a dominant gene that is not recognised by the Burmese Registration Policy, however there is increasing anecdotal evidence of its existence within the UK Burmese gene-pool provided by judges assessing Cream, Lilac and Lilac Tortie coloured Burmese at shows. A genetic test for the Dilute Modifier has not yet been perfected, but is likely to become available in the foreseeable future, in the meantime the Burmese BAC has resolved to monitor the situation until such a test is commercially available when cats of suspect colour can be tested to establish their colour genetic make-up.
8. Long-hair (L) – a recessive gene not present in the Burmese breed which is fundamentally a short hair breed, but included here for completeness. All Burmese cats are LL (ie short-hair).
Inhibitor (I) – not present in the Burmese breed, the Inhibitor gene radically reduces the production of melanin deposited along the hair-shaft and when present causes the cat to exhibit a silver base to each hair. All Burmese cats are ii (ie. Non-Silver).
9. Polygenes – these are collections of genes which modify the effect of the main dominant and recessive genes above. A build-up of polygenes creates a bigger effect, for example a collection of certain polygenes increases the length and density of the long-hair gene to create the Persian, and a build-up of polygenes serves to enhance the effect of the main colour genes, turning the effect of the orange gene from the sandy colour of the ginger domestic tom to the rich vibrant red of the Red Persian, British or Burmese. It is likely that a group of polygenes, some of which have a positive effect and others a negative effect on the main genes is the reason for variation in the degree of warms, coolness, richness or depth of colour in all Burmese, careful selection by breeders of breeding cats which exhibit the correct build-up of desirable poly-genes will generate the much sort pinkish cast in the Burmese Lilac or the desired warm rich milk Chocolate colour.
So, in summary, the genetics involved in the ideal Burmese cat are complex. Not only are there many interacting genes, but genes sometimes do not express themselves fully, or conflict with one another. They can also be affected by external factors, for example, the Burmese Colour Restriction gene is sensitive to air temperature allowing more melanin to be expressed in colder conditions and inhibiting melanin when warmer. Various polygenes, epigenetic factors, or modifier genes, as yet unidentified, are believed to result in different phenotypes of colouration, some deemed more desirable than others.
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