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The Genetics of the Bengal
You can quickly learn the basics of the genetics
that affect the coat of the Bengal cat.
However, before we get going, let me add one
proviso. The research into cat
genetics is continuing all of the time, and even in the last couple of
years new genes have been identified.
So if I am behind the times, or if you know more or better than I
do, I would love to hear from you so that I can update this page.
This page mostly concentrates on coat type,
colour and pattern. It does not
cover all of the genes affecting the coat, but concentrates on those
affecting the Bengal.
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How Genes Work
The first thing to understand is that all genes
come in pairs.
When an egg is formed it only contains one half
of the pair of the dam’s genes – the other half of the pair goes into a
different egg. Similarly, when sperm
is formed, each only contains one half of the pair of the sire’s
genes.
When the sperm fertilises the egg the two halfs
join together to form a pair of genes again – so the kitten (other than in
exceptional circumstances) always inherits half it’s genes from it’s dam
and half from it’s sire.
It is not true that the sire’s genes are
‘stronger’ than the dam’s genes.
After all, the sire inherited half his genes from his dam, and the
dam inherited half her genes from her sire – so how can they be? Both the dam and sire should take equal
credit for a ‘good’ kitten, and equal credit for a ‘bad’ kitten. It all depends on how the genes mix and
match.
There are different genes that affect the pattern
of the coat (spotted or marbled), and the colour of the coat (brown, snow, blue,
silver, chocolate, cinnamon), and the type of coat (long or short
haired). Each gene has a specific
job to do.
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Dominant and Recessive
Some genes are dominant and some are
recessive.
The pair of genes could be made up of two
dominant genes, or two recessive genes, or one of each. Where a cat has one dominant and one
recessive gene as a pair, then the effect of the dominant gene will always
affect the cat. The recessive gene
will (usually) be invisible.
For example the short hair gene is dominant, and
the long hair gene is recessive. So
if the pair of genes in a cat is made up from one short hair gene
(dominant) and one long hair gene (recessive) the cat will be short haired.
However, there are exceptions to this rule as
some genes seem to be more ‘strongly’ dominant than others. This is usually described as being
‘incompletely dominant’.
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The ‘Buzz Words’ – Homozygous and Heterozygous
Two very long words that have a simple meaning.
If a cat has a pair of genes of the same type then
they are ‘Homozygous’. So a long
haired cat, that has a pair of long haired genes is ‘Homozygous for long
hair’, and a short haired cat that has a pair of short hair genes is
‘Homozygous for short hair’.
If the cat has a pair of genes that are not the
same, then they are ‘Heterozygous’.
For example, a short haired cat could have one
short hair gene and one long hair gene – this cat is Heterozygous.
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Charting the Genes
A simple way to work out what kittens your cat might
have, is to build a simple chart, and work out the combinations of genes.
I’ll continue to use the short and long hair
genes, as they are the simplest example to start with.
Start by drawing a chart that is 3 boxes wide and
3 boxes deep. Ignore the top left
hand box. Now fill in the the top
row with the stud’s genes, and in the left hand column the queen’s genes.
In the example below, both the stud (at the top)
and the queen (at the side) have one short hair gene and one long hair
gene. The symbol for the short
haired gene is ‘L’ and the symbol for the long haired gene is ‘l’.
Notice that the dominant and recessive genes use
the same letter, but the dominant gene is in upper case (L) and the
recessive gene is in lower case (l).
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MALE
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Short Hair (L)
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Long Hair (l)
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FEMALE
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Short Hair (L)
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Long Hair (l)
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Now take the symbol from the left hand male box
(l), and combine it with the top one from the female (L).
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MALE
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Short Hair (L)
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Long Hair (l)
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FEMALE
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Short Hair (L)
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L L
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Long Hair (l)
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Now add the symbol from the left band male box
with the bottom one from the female.
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MALE
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Short Hair (L)
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Long Hair (l)
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FEMALE
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Short Hair (L)
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L L
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Long Hair (l)
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L l
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Now do the same for the right hand two boxes.
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MALE
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Short Hair (L)
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Long Hair (l)
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FEMALE
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Short Hair (L)
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L L
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l L
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Long Hair (l)
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L l
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MALE
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Short Hair (L)
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Long Hair (l)
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FEMALE
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Short Hair (L)
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L L
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l L
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Long Hair (l)
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L l
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l l
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You should end up with:
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MALE
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Short Hair (L)
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Long Hair (l)
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FEMALE
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Short Hair (L)
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L L
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l L
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Long Hair (l)
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L l
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l l
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Top left, you have L L – two short haired genes
(L) – this kitten will be short haired (homozygous)
Top right, and bottom left - you have one L and
one l – one short haired gene and one long haired gene – these two kittens
are short haired but carry long hair (the short hair gene is dominant, so
the long hair gene is ‘invisible’)
Bottom right is l l – two long haired genes – so
this kitten is long haired.
So the average that you would get from this
mating are half the kittens being short haired, but carrying long hair
(heterozygous), 25% being Long Haired (homozygous) and 25% Short Haired
(homozygous).
Remember though, that these are only
averages. Some eggs may die before
they are fertilised, some sperm may never get that far, and then fertilised
eggs may not survive. And you never
know which ones will actually go full term.
So don’t expect to always get one long haired
kitten in every litter of four. You
have to repeat several matings before the ‘averages’ start to show up.
You can use this chart to work out the coat type,
pattern or colour of any of the genes below – though the chart gets rather
big and complicated if you try to chart more than one gene at a time – as
you have to allow for every combination that might occur.
To work out the combinations of one gene, there
are four possible combinations (the male carries a pair, and the female
carries a pair). But to work out the
combinations of two genes together (e.g. marbled or spotted, and snow or
brown), there are sixteen possible combinations. As you might guess, the boxes get a bit
big and complicated, and it is easy to lose track if you try to do too many
combinations at a time.
Just as an example, here is a box where both the male
and the female are brown spotted, but where they both carry marble and
snow. Marble is recessive to
spotting, and snow is recessive to brown.
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MALE
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Spotted + snow
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Marble + snow
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Spotted + brown
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Marble + brown
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FEMALE
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Spotted + snow
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2xspotted genes
2x snow genes
= snow spotted
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1 spot + 1 marble
2x snow genes
= snow spotted
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2xspotted genes
1 brown+1 snow
= brown spotted
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1 spot + 1 marble
1 brown+1 snow
= brown spotted
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Marble + snow
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1 spot + 1 marble
2x snow genes
= snow spotted
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2x marble genes
2x snow genes
= snow marble
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1 spot + 1 marble
1 brown+1 snow
= brown spotted
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2x marble genes
1 brown+1 snow
= brown marble
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Spotted + brown
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2xspotted genes
1 brown+1 snow
= brown spotted
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1 spot + 1 marble
1 brown+1 snow
= brown spotted
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2xspotted genes
2x brown genes
= brown spotted
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1 spot + 1 marble
2x brown genes
= brown spotted
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Marble + brown
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1 spot + 1 marble
1 brown+1 snow
= brown spotted
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2x marble genes
1 brown+1 snow
= brown marble
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1 spot + 1 marble
2x brown genes
= brown spotted
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2x marble genes
2x brown genes
= brown marbled
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So out of the mating of two brown spotteds who
both carry marble and snow you would get (on average for 16 cats):
3 snow spotted,
2 of which carry marble
9 brown
spotted - 2 carrying snow, 4 carrying snow and marble, 1 carrying marble
and one homozygous
1 snow
marble
3 brown
marbles, 2 of which carry snow
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Bengal Genes
These are the main genes that affect the Bengal,
with an explanation of each of them.
As said previously, research is still taking place and new genes are
being discovered all the time, so if you know more, please let me know
(contact details at the bottom of the page).
I have included some genes that do not relate
directly to the Bengal, as they help clarify how
other cats differ.
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Dominant
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Recessive
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Notes
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A Agouti
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a
non-agouti
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Agouti is the tabby/patterned cat
Non-agouti is the self coloured (solid colour)
cat
A is dominant to a, though not always completely
- you can sometimes see the shadow of the tabby pattern on a solid
coloured black cat that is heterozygous (i.e. on one that is Aa)
a in combination with the Inhibitor gene (I) can cause smoke
(see more at the bottom of this page)
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B Black
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b
chocolate
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b is the chocolate gene – all of the black is
replaced by a rich chocolate brown
B is incompletely dominant to b
Bb can result in a black cat with rusty coloured
shading
b is incompletely dominant to b1
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b1
cinnamon
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b1 is the cinnamon gene – where the black is
replaced by a rich cinnamon brown
A cat that is b1 b1 will be cinnamon, but where the
cat is b b1, they are often a pale shade of chocolate, as b is not
completely dominant to b1
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C Full
Colour
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c albino
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The albino cat with no colour and pink eyes (not
relevant to the Bengal)
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ca
blue-eyed white
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The blue-eyed white cat (does not relate to the Bengal
– this cat is white all over)
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cs
siamese
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Ivory background, coloured points and blue eyes
-the blue-eyed snow (seal lynx point)
Note that reddish blue eyes may be a sign that
this cat also carries chocolate
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cb
burmese
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Ivory background, darker (sepia) coloured
points, with brown, yellow or green eyes (seal sepia)
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If you have a Bengal that
has one cs gene and one cb gene, then the two genes ‘mix’ – neither is
dominant or recessive to one another.
The result is the Seal Mink – with turquoise eyes. This combination of genes is referred
to as the ‘Tonkinese’ colour
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D Dense
Colour
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d dilute
colour
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Dense colour is fully dominant to dilute colour.
A combination of BBDD gives a black cat, but BBdd
is a blue cat
A brown cat (bb) with dilute (dd) is a lilac
A cinnamon cat (b1b1) with dilute (dd) is a fawn
A sex linked Orange
cat (OO) with dilute (dd) is a cream
The combination of Agouti (A) and dilute (d)
causes a cream base coat rather than the usual Agouti yellow base coat.
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Dm Dilute
modifier
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dm normal
dilution (maltese dilution)
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The Dm gene only takes affect where dd is also
present.
On blue, lilac and fawn cats with Dm = caramel
Red cats with Dm = apricot
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I Colour
Inhibitor
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i normal
colour
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The standard description of the Inhibitor gene
is that it is a completely dominant gene which inhibits all colour in the
coat – i.e. causes silver.
However, it appears to be either incompletely
dominant, or is affected by rufousness – as we have all seen the
‘tarnished’ silver who has some hint of brown in the coat.
A combination of Agouti (AA) with the inhibitor
(I) causes smoke in some cases.
Some believe that both the Inhibitor gene and the Agouti gene come
in varying ‘strengths’, and that an excess of Inhibitor with insufficient
Agouti causes the smoke.
However, it is possible that other, as yet
unidentified genes are coming into play.
See below for more details on silvers
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L Short
hair
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l long
hair
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The short haired gene is completely dominant to
the long hair gene. The sources I
have read say that ‘the length of hair is determined by selective
breeding’ – however this comment in itself indicates that another gene
(or genes) may be present which affect hair length – and the ‘selective
breeding’ is selecting cats with this other ‘hair length modifier’
gene(s).
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Mc
Vertical flow
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mc
circular flow
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The Mc gene gives a vertical stripe or pattern,
but the mc gene causes a swirling/circular pattern
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mz
horizontal flow
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Currently a theory only – believed to cause the
horizontal alignment of the pattern found only in Bengals and believed to
be inherited directly from the ALC
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Mi Not
glittered
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mi
glittered
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Another ‘theoretical’ gene – causing the glitter
on the Bengal coat. The designation of Mi is only
‘temporary’ – I have also seen this gene referred to as Gi or Gl.
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Rf Normal
colour
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rf rufous
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Originally thought to be a series of polygenes
(blending genes), the rufous gene is now thought to be a separate gene
that causes red in the coat.
There is still some work to be done here, as
another theory believes that the rufous colouring is caused by the
‘extension’ gene
However, as the amount of red in a Bengal coat
varies considerably from cat to cat, I am sure that most Bengal breeders
will be convinced that this gene may come in varying ‘strengths’, or is
affected by another gene that changes the amount of red in the coat.
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S White
spotting
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s no
white spotting
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Incomplete dominance in that Ss will have some
white spotting
SS =
Harlequin or Van > 2/3rds
white
Ss =
Bicolour 2/3rds
white
So what causes the locket? Is the locket caused by another
variation on this gene, that hasn’t yet been identified? Or is it just an
Ss with very little white.
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Sa Normal
hair
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sa
satin/silk fur
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Another ‘theoretical’ gene -
No or minimal undercoat, with a satin finish to
the coat
I has been suggested that this gene is another or
different cause for glitter (see Mi), however I think most Bengal
breeders will agree that this is unlikely as Bengals that have silky fur
with no undercoat are not always glittered.
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Sp
Pattern Interrupt
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sp normal
tabby (Classic or Mackerel)
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Now identified as a separate gene affecting the
tabby pattern by breaking up the pattern to cause spots rather than
lines.
It is still not known what causes the variance
in spot shapes and colours (i.e. rosetting)
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T Ticked
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t not
ticked
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The Agouti cat is a ‘ticked’ cat – that is to
say that there are bands of colour along the hair shaft. However, the number of and the width of
the bands varies considerably from breed to breed, and even within a
breed such as a Bengal.
So is there a ‘Ticked’ gene affected by a gene
that affects the width of the bands of colour??
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Ta Ticked
non tabby
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The dominant Ta gene produces a ticked cat
without the tabby pattern – such as the Abyssinian.
If a cat has a mackerel or blotched tabby pattern
then it must carry the double recessive ta ta.
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tb
blotched tabby
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Blotched (aka classic) tabby
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Wb Wide
band
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wb normal
band
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Determines the width of the colour banding on a
Ticked coat
May be the cause of clear coats in the Bengal
– believed to widen the Agouti band, and push the ticking off the end of
the hair shaft.
See table below as to how it works in
association with Inhibitor
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O Sex linked orange
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o not
orange
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I have only included this one because some of
the early Bengals did carry sex-linked orange (notably Millwood
Pennybank).
The male is an xy, and the femal is an xx, and
the o gene can only ‘attach’ to the x gene, so a male can only ever carry
one o gene, but a female can carry a pair.
xxoo = female not red or cream
xyo = male not red or cream
xxOo = female tortie/tortoishell
xxOO = female red (or cream with dd)
xyO =
male red
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Others
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Melanism
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A mutation associated with the non-Agouti gene
‘a’
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Flat Chest
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There are very mixed feelings as to whethere
this caused by a recessive gene or by environmental affects, or a mixture
of both
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Kinked Tail
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Possibly caused by a recessive gene
My personal opinion is that if the cause is
genetic, then there is a very close link between this gene and the one
that causes the Flat Chest
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Cleft Palate
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Opinion varies as to whether this is caused by a
gene, or by immaturity at birth.
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Combinations of Inhibitor, Wide Band and Rufous
Genes
These do not relate to the Bengal,
but may be of interest as they help understand how the wide band gene
pushes the ticking off the hair shaft.
It also shows that where the Rufous gene is
present, the Inhibitor gene is not completely dominant. In Bengal silvers
this is called ‘tarnishing’, but in other breeds, where the Rufous colour
is controlled and evenly spread, they are called goldens.
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Smoke
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aa I- Wb- Rf or
aa I- wbwb Rf
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A non Agouti cat with the Inhibitor gene and
only one, or no wide band gene and no rufous gene
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Silver Shaded
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A- I- Wbwb Rf
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An Agouti cat with the Inhibitor gene and one
Wide band gene and no rufous gene
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Silver Tabby
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A- I- wbwb Rf
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An Agouti cat with the Inhibitor gene and normal
banding and no rufous gene
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Chinchilla
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A- I- WbWb Rf
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An Agouti cat with the Inhibitor gene and pair
of Wide band genes and no rufous gene
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Golden Smoke
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aa I- Wb- rfrf
aa I- wbwb rfrf
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A non Agouti cat with the Inhibitor gene and
only one, or no wide band gene and double rufous gene
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Golden Shade
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