Beautiful Bengals




Thank you to Carol Hebden for allowing me to share her knowledge of Bengal Genetics. 



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.





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.




Dominant and Recessive Genes 



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’.



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.




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).





Male
Short Hair (L) Long Hair (l)
Female Short Hair (L)
Long Hair (l)

Now take the symbol from the left hand male box (L), and combine it with the top one from the female (L).


Male
Short Hair (L) Long Hair (l)
Female Short Hair (L) L L
Long Hair (l)

Now add the symbol from the left band male box with the bottom one from the female.


Male
Short Hair (L) Long Hair (l)
Female Short Hair (L) L L
Long Hair (l) L l

Now do the same for the right hand two boxes:


Male
Short Hair (L) Long Hair (l)
Female Short Hair (L) L L I L
Long Hair (l) L l


Male
Short Hair (L) Long Hair (l)
Female Short Hair (L) L L I L
Long Hair (l) L l l l

You should end up with:


Male
Short Hair (L) Long Hair (l)
Female Short Hair (L) L L I L
Long Hair (l) L l l l


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.


Male
Spotted & Snow Marble & Snow Spotted & Brown Marble & Brown
Female Spotted & Snow 2xspotted genes
2x snow genes
= snow spotted
1 spot + 1 marble
2x snow genes
= snow spotted
2xspotted genes
1 brown+1 snow
= brown spotted
1 spot + 1 marble
1 brown+1 snow
= brown spotted
Marble & Snow 1 spot + 1 marble
2x snow genes
= snow spotted
2x marble genes
2x snow genes
= snow marble
1 spot + 1 marble
1 brown+1 snow
= brown spotted
2x marble genes
1 brown+1 snow
= brown marble
Spotted & Brown 2xspotted genes
1 brown+1 snow
= brown spotted
1 spot + 1 marble
1 brown+1 snow
= brown spotted
2xspotted genes
2x brown genes
= brown spotted
1 spot + 1 marble
2x brown genes
= brown spotted
Marble & Brown 1 spot + 1 marble
1 brown+1 snow
= brown spotted
2x marble genes
1 brown+1 snow
= brown marble
1 spot + 1 marble
2x brown genes
= brown spotted
2x marble genes
2x brown genes
= brown marbled


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



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.


Dominant Recessive Notes
A Agouti a non-agouti 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)
B Black b chocolate 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
b1 cinnamon 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
C Full Colour c albino The albino cat with no colour and pink eyes (not relevant to the Bengal)
ca blue-eyed white The blue-eyed white cat (does not relate to the Bengal - this cat is white all over)
cs siamese 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
cb burmese Ivory background, darker (sepia) coloured points, with brown, yellow or green eyes (seal sepia)
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
D Dense Colour d dilute colour 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.
Dm Dilute Modifier dm normal dilution (maltese dilution) 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
I Colour Inhibitor i normal colour 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
L Short Hair l long hair 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).
Mc Vertical flow mc circular flow The Mc gene gives a vertical stripe or pattern, but the mc gene causes a swirling/circular pattern
mz horizontal flow 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
Mi Not glittered mi glittered 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. The glitter is caused by the tip of each hair shaft being hollow, so that the light passes through the hair tip.
Rf Normal colour rf rufous 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, the amount of red in a Bengal coat varies considerably from cat to cat, and not in direct relationship to the width of the colour bands. My personal opinion is that this gene may come in varying ‘strengths’, or is affected by another gene that changes the amount of red in the coat.
S White spotting s no white spotting 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.
Sa Normal hair sa satin/silk fur 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.
Sp Pattern Interrupt sp normal tabby (Classic or Mackerel) 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)
E Extension Gene Determines the width of the colour banding on a patterned (agouti) coat 
O Sex linked orange o not orange 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

Birth Defects

Flat Chest There are very mixed feelings as to whether this caused by a recessive gene or by environmental affects, or a mixture of both.
Kinked Tail Possibly caused by a recessive gene
There is a possibility that there is a link between tail faults and spina bifida.
Cleft Palate Opinion varies as to whether this is caused by a gene, by immaturity at birth, or a congenital birth defect caused by some outside influence during pregnancy.

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