WIDE BAND GENE INVESTIGATION INTO “GOLDEN COLOURS”
This page pulls together investigations into the role of the wide band gene in different breeds and its role in “Copper” British Shorthair, Golden (Sunshine) and “Bimetallic” Siberians and in the Golden Tiger. Rather than duplicate information on multiple pages, this page will concentrate on the genetics and phenotype rather than the history and pedigrees. Information has been provided by Suzanna Multhaupt (Berlin, Germany – Dorofei Siberian Cats), Linda Petersson Wahlqvist (Gothenburg, Sweden), Marina Bessergeneva (Volgodonsk, Russia – Golden River Cattery).
In brief, there are only two pigments in cats: red (phaeomelanin) and black (eumelanin) which are laid down in alternating bands on ticked hairs or along the whole length of non-ticked hairs. All other colours are due to dilution (causing misshapen pigment molecules) or degrees of reduced pigmentation. Rufism is the reddish tint found on eumelanin-based silvers where phaemelanin bands are not completely suppressed by the Inhibitor gene. There are currently no DNA tests for silver, gold or rufism.
In tipped animals, the (poly)genes for ever wider “wideband effect” have been selectively bred for a long time. Chinchilla and Silver Tabby Persians have been selected for the most extensive white basal zone of the hair for around 150 years.
In the Siberian breed, breeders have worked for around 100 years to achieve maximum expression of Agouti. Therefore, in the Siberian and similar breeds, the kittens are born black and blossom into gold as they develop their adult coat.
In the British and Persian (tipped), kittens are born light-gold, almost milky white. As they mature they become brighter and the colour becomes more saturated. The kittens with the whitest underparts appear to become the brightest coloured adults.
Research Programmes: Silver and Golden at Lyons Feline Genetics Laboratory
Phaeomelanin – red/orange/yellow pigment
Eumelanin – black-based pigments (black, blue, chocolate, lilac)
Copper – informal term used to describe a particular phenotype in British Shorthairs
Sunshine – term sometimes used to differentiate Siberian Golden from Persian/British Golden
UU – hypothetical gene/polygene complex that modifies ticked tabby pattern
At least two different genes are suspected of influencing the silver and golden coat colours found in many cat breeds. Interactions with other genes, and polygenes modify the effect.
The dominant Silver (Inhibitor (I,i) reduces or eliminates phaeomelanin (yellow pigment) production in the cat’s hair. On agouti hairs there are dark bands, but the light bands are changed from yellowish to white.
Wide-band (Wb) affects the length of the bands on agouti hairs. It is very variable, causing many short bands or fewer longer bands. Breeders have selected for fewer longer bands. Cats with fewer longer bands appear as chinchillas in silver cats and as goldens in non-silver cats. Wb is suspected to be recessive. It is possible that the variable Wb effects are due to multiple genes at different loci (positions on chromosomes) as shown in the diagram below.
Ticked Tabby masks any other tabby patterns. Ticked Tabby without Wb gives the pattern found in Silver Abyssinians. Ticked Tabby + Wb gives Chinchillas. Ticked Tabby with extreme widebanding gives very pale Chinchillas, almost pure white. When Ticked Tabby is absent, the tabby pattern shows up. Silver Tabbies have the Inhibitor Gene. Golden Tabbies have Wb but no Inhibitor, giving a golden background with darker markings.
In addition to Inhibitor (silver), another gene is inherited. Wb works only with the agouti gene. What about another theoretical called (4 different names for same gene) Silver Bleaching (Sv), Eraser (Er), Unpatterned (U) or Bleaching (bl). This gene works with both Agouti and non-agouti genes. For simplicity, I will call it Unpatterned (U).Non-agouti + Unpatterned + Wide Band – this cannot become Golden Smoke, but will be solid colour with unpigmented fur near the skin (which often happens).
Another theory is the Golden Epistatic Gene or an “Ay” allele of the Agouti gene that is dominant over A. This is seen in gold agouti mice and sable dogs. It causes the formation of yellow-golden lower zone of the hair - with a black tip. An ideal golden chinchilla would be: Ay-TaTa ii UU WbWb (Epistatic Golden + Ticked Tabby + recessive inhibitor + Unpatterned + Wideband)
What if U is a complex of polygenes? There is an older theory of silver (and golden) that involves 2 interacting genes called Silver Bleaching (cancels rufousing in eumelanin colours, but not so much in phaeomelanin colours - leaving behind warmer tones) and Eraser (causes silver at the base of the hair).
Agouti + Silver Bleaching without Eraser - shaded and tipped cats with a coloured band, instead of a bleached band, near the skin. This is not seen in cats.
Non-agouti + Silver Bleaching without Eraser - cool-toned (unrufoused) solid colour cats.
Non-agouti + Silver Bleaching + Eraser - Smoke pattern.
If smoke cats heterozygous for both silver and eraser (sv and er) were bred together, they should produce some solid colour offspring (svsv erer).
If shaded or tipped cats heterozygous for both silver and eraser (sv and er) were bred together, they should produce some cool-toned full colour ticked tabby offspring (svsv erer) i.e. less rufoused than an Abyssinian.
Eraser + Silver Bleaching causes silver at the base of the hair.
Agouti + Eraser without Silver Bleaching (Er- svsv) – warm-toned pale ticked tabbies, golden base colour shade rather than a reddish one i.e. shaded goldens and they are only recognised in eumelanin (black-based) colours not in red-based colours. Red-based versions are visually similar to red or cream ticked tabbies. This theory means golden tabbies would result from breeding together silver tabbies that carry the recessive sv allele.
A golden tabby (svsv) with dominant Er would be golden tabby shell or shaded depending on the amount of pigment present. A golden tabby with only erer would not have depigmented hair roots.
Non-agouti + Eraser without Silver Bleaching (Er- svsv) - golden smoke, but golden smokes don't exist in reality. This means the Er + Sv theory is also flawed, or that these are not 2 genes that can be inherited separately.
The genetic basis of the gold colour is the same for the Siberian breed and the British Shorthair, Kurilian Bobtail and the Maine Coon, but there is a wide variety of transitional forms and the interaction of agouti with inhibitor and/or various polygenes gives the wide variety of golden colours (though some breeders refuse to accept that "ultra" phenotypes exist). The agouti gene consists of 5 structural units (domains), only one of which directly encodes a protein that blocks the receptors, and 4 other regulate its expression. In particular, one of those domains contains a promoter ("trigger" gene element), responsible just for the cyclicity of gene activity. Another domain contains a promoter that determines the selective dorso-ventral activity of the Agouti gene. In other words, the activity of this gene in the cells of the hair follicles on the spinal surface of the animal’s body is lower than on the abdominal surface. This means that the dorsal part of the body is dominated by ticked fur, and the abdominal surface is dominated by a lighter (phaeomelanin) fur. Point mutations of the Agouti gene complex cause an increase in the amount of black pigment (the so-called hypomorphs and amorphs) are usually recessive in nature and can be multiple mutations.
As a result there is a wide array of completely different colours: yellowish-brown, brown, yellowish-grey, charcoal-grey, even olive. The markings can be high-contrast or low-contrast against the background colour. Chest, abdomen and inner sides of the legs can be light yellow, reddish or pale grey. The zoning of hairs presents a variety of options: Shorthair cats usually have either one (or occasionally two) yellow band on the hair or have a combination of yellow and grey bands. Long haired cats up to 8 yellow bands on the hair. The hairs of the markings and the background also varies, ranging from pure-black hair to yellow or grey-yellow-grey in some areas.
WIDE BAND GENOTYPES IN TIGERS
In Cell Research, 10 March 2017, a letter entitled The Genetics Of Tiger Pelage Colour Variations written by Xiao Xu, Gui-Xin Dong et al described Wideband in tigers. The white tiger coat is due to an autosomal recessive gene on the W locus i.e. white tigers are genotype w/w. This is different from the dominant Inhibitor gene found in domestic cats. The golden colour is an autosomal recessive trait called Wideband, referring to a wider central part of the hair shaft. Golden tigers are therefore wb/wb genotype. Stripeless white tigers are recessive for both of these genes i.e. w/w, wb/wb.
The mutation called p.A477V in gene SLC45A2 switches the background colour of agouti hairs from normal orange to white. On orange tigers, the agouti hairs have dark tips and bases and bands of phaeomelanin in between. On golden tigers, the agouti hairs have dark tips and bases, but have much wider bands of pale colour and narrower bands of red pigment between them. Where the stripes are reddish brown rather than black, it appears that wideband has extended the phaeomelanin synthesis phase during the hair growth cycle. In domestic cats an extension gene is also posited for this effect. In 2017, the only confirmed mammalian wideband gene was a mutation of the Agouti Signalling Protein (ASIP) gene. ASIP causes switching between eumelanin and phaemelanin production during hair growth. It was not known whether ASIP was the wideband gene in golden tigers.
A mutation in the CORIN gene was found to be specific to golden and stripeless white tigers. CORIN suppresses the agouti pathway. This was confirmed using CORIN knockout agouti mice. All golden and stripeless white tigers sampled were homozygous for the CORIN mutation. All orange and striped white tigers sampled had the wild-type CORIN genes though some also carried the recessive mutant version. Genotype analyses of CORIN p.H587Y and SLC45A2 p.A477V confirmed that the individual or combined effect of these two mutations explained the 4 tiger coat colour variations (normal, striped white, stripeless white, golden). Wild-type CORIN regulates melanin production by suppressing the activity of ASIP.
Theory: The p.H587Y mutation might impair the function of CORIN and elongate the working period of ASIP, resulting in the wider bands on the golden tiger hair. Their study demonstrated that CORIN is a feline wideband gene. Because CORIN inhibits ASIP in melanin production, reduced function of CORIN or increased function of ASIP could both cause a wideband effect in mammals, demonstrating that there may be multiple genotypes causing the “wideband” effect in mammals. Stripeless white tigers are homozygous for both SLC45A2 p.A477V and CORIN p.H587Y mutations, indicating that “white tiger mutation” + “golden tiger mutation” may reduce melanin production throughout the whole coat. However, the regulation of ASIP activity by CORIN p.H587Y alone (or along with the effect of the SLC45A2 mutation) does not fully explain the colour change of stripes in either golden or snow white tigers.
EMS COLOUR AND PATTERN CODES
BSH (BRI) - British SHorthair
BLH – British Longhair
EXO – Exotic Shorthair
PER – Persian Longhair
SIB - Siberian
n - black ("n" comes from the French “noir”) |
a - Blue
b - chocolate
c - lilac
d - red
e - cream
g - blue tortie
h - chocolate tortie
j - lilac tortie
w - white
s - Silver
y - Golden
11 - shaded (merged into tipped/chinchilla in BSH/BLH, shaded in PER)
12 - shell (merged into tipped/chinchilla in BSH/BLH)
21 - unspecified tabby
22 - blotched tabby
23 - mackerel tabby
25 - ticked tabby
01 - van
02 - harlequin
03 - bicolour
09 - any other amount of white
So ny25 is decoded as black + golden + ticked tabby
RUFISM VS GOLDEN (BRITISH SHORTHAIR/LONGHAIR, PERSIAN & EXOTIC)
The most common debate (which can get really nasty) is that golden is just Rufism or is poor suppression of pigment by the inhibitor gene. Some go so far as to say there is no such thing as golden, it is just a fancy word for a black tabby. This is made worse because some breeders register and sell black tabbies as golden tabbies because it sounds fancier. Contributors to this page are helping collect DNA samples to unravel this and to develop a DNA test for Silver and Gold.
True Rufism – as opposed to Gold - is the incomplete dominance of silver over "non-silver", which shows up mainly on the undercoat, which should ideally be white everywhere. These areas of "non-silver" are often located chaotically - a stain on the neck, on the back, on the head. If yellowing is found on the hair tips, but not on the undercoat, this is not Rufism! Only homozygous silver does not give Rufism. Gold cats are genetically black, and have both eumelanin and phaeomelanin visible at the same time because these are laid down in alternating bands.
One Theory (not proven): Rufism is the predominance of phaeomelanin. In gold colours, breeders select animals where phaeomelanin (Rufism) predominates. In silver colours, selection is made for the exclusion of phaeomelanin and the production of eumelanin only. The silver gene has a greater effect on eumelanin and a lesser effect on phaeomelanin. When mating a gold cat to a silver one, the silver gene does not cope with the phaeomelanin zones in the hair resulting in areas of non-silver colour. These zones may be spots on the sides, back, muzzle, and paws. Sometimes there is a dorso-versal division where the chin, chest, and belly are golden colour (this colour division is seen on ticked cats such as Abyssinian). If there is a red zone on the tips of the hair, then this is not considered Rufism. Mating a cat selected for black pigments (that can be suppressed by the inhibitor) to a cat selected for red/gold pigments (which cannot be suppressed so well) gives unpredictable results. There is a “conflict of interest” between the colours! A lot depends on whether the silver parent is homozygous and how strongly the other parent expresses and passes on phaeomelanin.
COPPER (ULTRA WIDE-BAND) BRITISH SHORTHAIRS
Tipped and Shaded Golden British Shorthairs are also known as Golden Chinchilla and Golden Shell. The informal term "copper" was adopted by Linda Petersson Wahlqvist to describe tipped cats with white toes, white undersides, golden colour with the dark tips (e.g. black or blue) restricted to the tail tip and an absence of dark nose-liner. This phenotype deviates from the standard for tipped cats, but is becoming prevalent in Russia and in some German lines of British Golden Shorthairs. In Russia, there is a debate on whether to change the Golden Chinchilla colour standard to match the “copper” cats i.e. brightened (whitened) breast and belly? The argument is that silver chinchillas have the same colour distribution, but we do not see it because "silver" is the absence of pigment! Gold chinchillas from completely different lines have the same effect of “whitening" the breast and other parts, which favours the theory that this is not a mutation inherited from a single ancestor. It is the work of several genes together.
Some Russian breeders have produced golden cats so pale (the colour of set honey), but with black tail tips and black paw pads, that they have called the colour "amber" even though it is not related to the Norwegian Forest Cat amber colour. They have labelled it a colour in development to set it apart from the normal golden colour.
Shaded and tipped (shell/chinchilla) are due to the dominant Inhibitor gene (silver) + presence of Wide Band + the Ticked Tabby pattern. Although "Wb" is treated as a single gene for simplicity, it appears to act as polygenes with an additive effect. In ticked tabby cats without silver, Wide Band restricts the pigment to the end of the hair leaving a pale golden band between the skin and the pigment. Through selective breeding, this effect has been maximised. The variability of the wide band suggests we should talk about Wb, Wb+ and Wb++ to describe cats with normal, intermediate and greater degrees of Wide Banding. One opinion is that "Golden Chinchilla" without the "milky-white" chest is really a shaded colour (not a tipped colour) where black pigment at the hair tips is maximally transformed into red-brown. The “copper” phenotype has a same sharp dividing line between reddish colour (genetically black, but modified by wide band gene(s)) and the milky-white underparts. This is why “copper” is believed to be the same mechanism as extreme Chinchilla (where the reddish pigment is completely suppressed).
The appearance of this phenotype was investigated by tracing the family trees of cats that displayed it (Copper Phenotype in Tipped British Shorthairs (Ultra-Wide-Band)). This showed that there was no single mutation, but an interaction of mackerel tabby (ny25) with chinchilla (ny11) and most likely an accumulation of Wide band polygenes. Alongside the "copper" phenotype there are chinchillas where the cats looked white except for the eye colour and paw pads. This shows that the Ultra Wide-Banding operates on cats with and without silver. Silver cats without Wide Band are cool-toned ticked tabbies. Golden (ticked) kittens can be born very dark, but become lighter as they mature.
What do ultra Wide-banded tabby-marked cats look like? i.e. how does the ultra wide banding affect non-ticked cats? It seems to turn the markings to gold and the only evidence of the black marking colour is seen at the tail tip and on the paw pads.
In tipped cats there has been selection for an increase in depigmentation, thus increased/longer depigmented bands. In “coppers” the increased depigmentation is milky or peach-gold. The golden zone "overlaps" unnecessary ticking on the hair. Tipping with ultra wide-band is “hidden ticking” all the colour zones, except for the hair-tip, are masked, although the genes determining them are still present. Polygenes further affect the colour. To get a "copper" requires full activity of polygenes to remove pattern i.e. “chaos” and “band frequency” genes (all are recessive and must be homozygous). For convenience, consider “chaos” + “band frequency” to be a single trait designated “U”. Copper has the theoretical genetic formula A-UUWbWb++ (Agouti + homozygous U + homozygous extreme wideband).
SIBERIAN GOLDEN (SUNSHINE)
The Siberian is recognised in many colours and patterns. Some registries recognise the "golden series". This is not recognised as "golden" by Britain's GCCF. Siberian "Golden Tabby (with or without white)," Golden Tortie Tabby (with or without white)," "Golden Shaded" etc are not viewed as a genetic colour, but as an expression of Brown Tabby due to wide agouti banding on the hair shafts which limits the black banding and gives a warmer, brighter tone. This means that Siberian cats registered as "golden" by FIFE or TICA are re-registered as brown tabby (etc) when transferred into GCCF. The relevant EMS codes are ny22 for Black Golden Classic (blotched tabby) ny23 for Black Golden Mackerel and ny24 for Black Golden Spotted. Ticked tabby (code 25) is not permitted.
Siberian breeders posited the term "Sunshine" so that this gene (or polygene effect) can be discussed and traced in pedigrees without confusing it with the Goldens born from lines with silver ancestry. “Sunshine” would refer to golden-coloured cats without silver ancestry. Siberian goldens may also be due to Wb inherited independently of the Inhibitor gene, but this does not explain the existence of “bi-metallic” cats which have both silver and golden colours simultaneously present.
In Persians, Exotics and British Shorthairs, golden seems to result from Wide band gene(s) and many of the cats have silver ancestors (dominant Inhibitor gene) because the wide band effect was selectively increased when breeding for pale chinchillas. There is a misconception that when a cat with a silver parent isn't silver, it must be golden by default. In Siberians, the Golden/Sunshine colour is inherited recessively. It brightens the agouti (ticked) areas of the coat. The colour seems to have arisen in a breeding programme in Russia. Because the "golden" Siberians don't change from black/blue to a golden colour, it is not an Amber or Russet (extension gene) mutation.
Suzanna Multhaupt has been looking into the golden colour and provided further information (2017). The true black golden tabby Siberian is free of shading and free of silver influence. Characteristic honey-golden markings come in classic (blotched), mackerel and/or spotted tabby but the undercoat is golden in all cases with the tip of the hairs black (probably Wb). So depending on the season, the coat will appear darker or lighter. The kittens are born very dark. Distinguishing factors are jet-black paw-pads with long fur between the toes, black eye-liner and green eyes. The nose is pink and has no pigmentation. Lips, too, are pink. The chin and chest are white but not solid coloured. She has found it almost impossible to get a "pure" black golden from non-black-golden parents.
As soon as you cross a black golden with any other colour, agouti or non agouti, the golden undercoat disappears and you get interesting tabby offspring but no black-goldens.
At birth, Golden/Sunshine Siberians resembled the early stages of the amber (ee) colour change in Norwegian Forest Cats caused by a mutation of the Extension gene. However, the Siberian cats tested negative for the amber gene. The nose leather is pinkish unlike that of a tabby cat. Where Golden/Sunshine occurs in cats with the “O” (red) gene, the red colour is brighter and the paws are lighter. The absence of pigment in the sunshine tabbies extends beyond the edges of the nose leather so they have no nose-liner and have whitish fur at the bottom of the nose.
Suzanna feels that the gold/silver colouring found in BSH/BLH has nothing in common with the golden colour of the Black Golden Siberian and this is supported by the existence of “Bi-metallic” Siberians. She wants to help isolate the genetic sequencing of the pure SIB Black Golden. Once that is done, it should be possible to compare sequencing with phenotypically similar cats of other breeds to see if the same mutations are present.
"Bi-metallic" is an informal term for a visual effect, while "sunshine" is a suggested gene name. In Siberian Cats, sunshine-silver produces the bi-metallic pattern. Some Siberian cats had both silver and golden areas of fur and were dubbed “bimetallic.” The effect is greater than rufousing or breakthrough colouring sometimes seen in silver tabbies. In some cats the golden areas increased as the kittens matured. The nose leather is pinkish unlike that of a tabby cat. The absence of pigment in the sunshine tabbies extends beyond the edges of the nose leather so they have no nose-liner and have whitish fur at the bottom of the nose.
Research by Eleonora Ruggiero into the pedigrees of Siberian Cats brought found that golden tabby Siberians can be born to non-golden parents. This means the gene was recessive and only expressed when two copies are inherited. Bimetallic females were often registered as tortoiseshell, but didn't breed as a tortoiseshell as they lacked the red (O) gene (evident when the paw-pads are examined and are not reddish). Their nose leather was dark pink, unlike the nose leather of tabby or genetic tortie cats. Many bimetallic Siberians appeared to have close Polish ancestry. Some black silver tortie tabby Siberians may be bimetallics (silver tabby + golden/sunshine).
BIMETALLIC BRITISH SHORTHAIRS
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.)
RUFISM VS BIMETAL
Bimetallic is an informal term for a visual effect. For cats where silver and golden are expressed in a pattern like that of a black-and-tan dog. The chin, chest and underside (extending to part way up each side) are golden. The upper parts are silver. In BSH & BLH this may be an extreme form of Rufism giving a particular phenotype. Establishing a DNA test for Inhibitor and Wide Band will help understand this.
ADDITIONAL NOTES ON POSSIBLE GENOTYPES
In Siberians, gold is formed to a greater degree by expression of Agouti + Wb, while in the British, Persians, Exotics, the complex = Agouti + Wb + UU and possibly many more are involved. (UU means homozygous for hypothetical genes that change agouti banding). To get a fuller picture, it is necessary to compare gold in other tipped breeds
Good quality tipped cats are ticked tabbies, but they have the lower dark part of the hair erased of colour by Wb + UU. This means tipping is a kind of ticking. Another observation is that two homozygous ticked tabbies do not produce tipped offspring. Tipping is semi-dominant even over ticking. Those that combine ticking and tipping are sometimes nicknamed "hedgehogs" and it can be difficult to understand which colour is ticked or tipped.
ADDITIONAL NOTE ON "COMMON ANCESTOR POLAR JENKO"
According to a breeder, Viola vom Wahrberg, who links many pedigrees to Polar Jenko, was not actually a daughter from Jenko. Jenko did not carry dilution. The breeder also had another young male at this time named Marvellous Rembrandt. And the cat had 6 kittens, 3 were blue-golden and 3 were black-golden (grey colour). It could be seen that the 3 blue-goldens were from Marvellous Rembrandt - he was definitely dilute carrier. Jenko never gave dilution, but point cats. Jenko never gave reddish (copper) coloured kittens. But by generations the colour got warmer. The first one in many opinions to give the "copper" colour was Marvellous Radetzky.
WOODS LAMP (UV LIGHT) TO IDENTIFY SILVER AND GOLDEN AREAS
one proposed method to separate Silver from Golden used the Woods Lamp (UV light). Such lamps in veterinary clinics determine the presence of ringworm. It was initially thought that in silvery colours, the fur closest to the skin, and that on the ears and muzzle glow blue. In golden colours the fur supposedly glowed pink/red. At first it was though that UV light could be used to differentiate between Golden and Rufism, but in Russia this method has now been discarded due to unreliable results.
BIMETALLIC-TYPE EFFECT IN AN AMERICAN SHORTHAIR
Sometimes the colour appears to change as the fur grows and may not be due to an extension gene mutation. This American Shorthair is genetically silver tortie but looks like brown/chocolate silver tabby or a tabby with mink/sepia colour restriction. She was born dark-coloured and the golden areas became prominent later. The father is a silver classic tabby (i.e. black marked) and the mother is cameo (red-silver) and white. Although the American Shorthair is accepted in all colours and has an open studbook, there is no known sepia (Burmese colour restriction) or chocolate in this cat’s pedigree. She was bred by Alhattab cattery in Kuwait and is CFA registered.
The inhibitor gene is less effective on red pigment than on black pigment, which means that a silver tortie can seem to have a mix of silver and golden background colour. The apparent brown colour could be due to an even mingling of red and black with a lot of rufousing, rather than clearly defined red and black areas. The father appears to have some tarnish (rufousing). However the development of the colour and the visual suggestion of a pointed cat is unusual. These come from Russian lines.