INHIBITOR GENE: BIMETALLIC BRITISH SHORTHAIRS
Many thanks to Martina Gottwald for photos and pedigree information on this page. "Bi-metallic" or "Bimetal" describes a visual effect where both silver and golden are present on in the coat at the same time, but is more than normal rufism.
Bimetallic refers to a silver cat that has full expression of rufism on the belly (which can be carried as a recessive trait) as is most commonly seen in Abyssinians. It shows to best effect in ticked/shaded cats. In breeds where the ticked pattern is not accepted, it shows to best effect in mackerel pattern cats, especially with a broken mackerel pattern in combination with high grade silver.
Martina Gottwald has been breeding British Shorthairs for 23 years and has found the bimetallic trait in some breeding lines. Although most German breeders prefer not to acknowledge it, it seems likely that some champion “golden" tabby and “shaded” may be genetically different, for example the sunshine or bimetallic trait. Independently of Linda Petersson Wahlqvist and Marina Bessergeneva she wondered if many European and Russian Champions over the last 15 years might be in the wrong colour classes at the shows because they are not conventional Golden Tabby/Shaded/Shell because the hair-tips are not black and the border of the nose is not coloured. Independently of my own linechasing on “Copper” British Shorthairs and British Longhairs, Martina suggested the bimetallic trait was widespread in European and German lines.
Tinjas Silver Sally Sunshine (either A_Bb(1 or 2) Cc Dd ii genotype) was born as a “black silver” but developed the strange mix of silver and golden between the third week and the fifth month of her life. She is pure British Shorthair over many generations and her parents are unrelated (note – the registry allows Scottish Straights to be registered as British Shorthairs). She is intermediate between silver tabby and shaded and was a test mating to investigate the bimetallic trait. Her paws are black underneath and she has dark eyeliner – the same as seen in black golden (sunshine) Siberians. Intermediate between tabby and shaded/tipped is common when only one of the parents is tipped.
Her parents are Lilac Golden Tabby Spotted (Tinjas Kleine Tulpe) x Seal Silver Shaded Point (Wittekind Point of Curchechi – British Shorthair). Neither showed anything strange, but her grandmother (on dam’s side) Mamajejos Ornella is Lilac Golden Tabby Point and probably also bimetallic. Ornella has no dark border around the nose. Black Golden (Sunshine) Siberians also have no black border around the nose; this is because the bleaching factor which makes the turns black to caramel or cream is stronger around the muzzle and mouth and removes all pigment. At first she appeared to be Lilac-based Caramel Golden Tabby Point, but she now appears to be the strange bimetal colour, not caramel. Ornellas litter-brother, Otis, is blue golden tabby point and possibly bimetallic.
Note: Tinjas Kleine Tulpe is registered as British Shorthair, other registries would call her Scottish Fold Straight. This page is concerned purely with colour genetics not registry policies.
Lilac Golden Tabby Spotted – EMS code cy 24. Genotype Aa bb1 dd tsp tbl II
Seal Silver Shaded Point – EMS code ns 11 33.
Depending on registry, Gold Tabby Point may be considered Seal Point with widebanding.
Tinjas Silver Sally Sunshine littermates were a male Black Silver Shaded Point and a female Black Silver Shaded Point. For Tinjas Silver Sally Sunshine, DNA samples will be sent to Leslie Lyons to compare to DNA from “regular” golden and from “coppers”. Martina also did a mating of Silver to Gold point and the results are similar – this cat is a silver tabby. The mother was heterozygous for silver and heterozygous for agouti. Further linechasing finds that the bimetallic cats, though rare or dismissed a rufism, seem to occur in lines that also produce copper phenotype cat, indicating a wide-band effect.
The bimetallic trait may have appeared as a side-effect of selecting for intense blue eye-colour in Colourpointed British Shorthairs. Wittekind Point of Curchechi (Seal Silver Shaded Point ) has very highly pigmented blue eyes, possibly due to polygenes for colour intensity inherited from his Chinchilla Persian ancestry; silver-pointed and golden-pointed cats often have deeper colour blue eyes than pointed cats without silver ancestry. Tinjas Mr Snowman de Baer (Scottish Fold chinchilla point) bred from Tinjas Zaubermaus de Baer (Chocolate Golden Tabby Point) x Wittekind point of Curbechi also has the same deep eye colour. As does Tinjas Silver Polarbaer (from BSH x BSH).
Black tabby and Golden tabby have the same standard except for eye colour – golden tabby has green eyes. The eye colour in Golden tabby could be different because of 50+ years of selective breeding for the gene/polygenes that cause wide-banding that dilutes the genetic colour. In some golden tabbies the pattern contrast is so good that it’s hard to know if wideband is present. (In pointed cats, to get the intense eye colour without introducing the silver factor means using a golden-point with good eye colour. The other side of the coin is that working for this eye colour produces non agouti cats that develop green eyes at maturity rather than copper eyes.)
There is a close relationship between these cats and those in pedigrees of the "copper" phenotype described at Copper Phenotype in British Tipped Shorthairs