PIEBALD SPOTTING gene S Gene S is responsible that the coat colour gets white patches. It is dominant over its companion s. Therefore gene S must be present only once to see its expression that a coloured coat gets white patches. Note: Gene S is said to be incomplete dominant, that means that the usually exspected ratio of 3:1 is turned to 1:2:1. Usually you can't see a difference between the homozygous and the heterozygous in the phenotype, with incomplete dominance you can see a difference in the phenotype, in our case you see a difference between Van, Harlequin and Bicolour pattern.	Solid colour Gen s Gene s is recessive to gene S. Your cat must have ss that its coat doesn't show white patches.	Possible gene combinations SS homozygous Van - in some federations these cats are called Harlequins (that means there are recognized only Harlequins=Vans and Bicolours). Cats carrying SS are used for breeding Bicolours, because all their offsprings will be at least Bicolours. Ss heterozygous Harlequin and/or Bicolour ss homozygous for being without white white patches Such cats will never produce Bicolours.
1 2 3 4 5 6 7 8 9 10   Nr. 1 is a solid coloured cat (ss ww) and Nr. 10 is a complete white cat (W-). Between Nr. 2 and Nr. 9 there are all ranges of piebald spotting. For showing purposes Nr. 4 and 5 would be a Bicolour, Nr. 6 to 8 would be a Harlquin, Nr. 9 would be a Van.
If you want to know which Bicolours are possible, then klick here.
Have a look also on the Crossing table for Bicolour.

What is a Van ? What is a Tricolour ? What is a Harlequin ?
What is a Calico ? What is a Parti-Colour ?

The most popular breed known as Van is the Turkish Van, this cat has a white body, white ears and white legs, on its head it has 2 colour patches on top of the head near the base of the ears and the tail is fully coloured.
Exactly this pattern is called in some federations a Van pattern (homozygous SS) and you may find this pattern also in Persians and Exotic, in the Maine Coon and Norwegian Forest, in British Shorthair and Europeans, in the Rex cats, etc.
A Harlequin is something inbetween a Van-pattern and a Bicolour. It has some colour patches on its body or its legs.
To make it confusing, in some federations the Vans are called Harlequins, that means there are only two patterns recognized the Harlequin and the Bicolour, while in other federations there are 3 patterns recognized, the Van, Harlequin and Bicolour.
A Bicolour has mostly the back fully covered and may show 1 white patch on the back, while the chest and stomach is white, which might go up to the flancs. The head including the ears shows colour and white. Ideally the face should show a white flame, and around the neck should be a white necklace. Legs and tail can be coloured with white patches.
In some federations tortie cats with white patches are called Tricolour - f.e. black tortie with white or bluecream with white, in other federations these cats are called Calicos.
In some federations cats are called Parti-Colour which are either tortie or tortie with white.

When you read already about gene W for entirely white cat you read about that theory that gene W together with blue eyes is the source for inheritance of deafness. That's one theory. Another one is that gene S, the gene for piebald spotting, together with blue eyes is the source for inheritance of deafness. According to this theory a lot more cats would be involved with the problem of deafness.
If you think about the dogs where more than 40 breeds are likely to inherit deafness, this theory gains plausibility.

If you're interested in that theory visit Orca Starbuck's article about genetic.
You may also find another interesting article dealing with this subject at Lorraine Shelton's page.

How can this theoretical knowledge be used for the breeding practice ?

You want to breed Bicolours, but have only a solid female.

You mate the female with a Bicolour male.
Your female is black and doesn't carry chocolate or cinnamon: BB D- oo ss. The male is blue and white and also doesn't carry chocolate and cinnamon: BB dd oo Ss.
Note, if the male doesn't show a real Van pattern, we must assume that it is heterozygous for Piebald Spotting (Ss).
Do you think we will get Calicos ? Let's look.

Example 2

As we have seen in example 1 we must use a male which has red or cream. So we try it again with our female and mate her with a cream and white bicoloured male: BB dd Oy Ss.

Example 3: Which male can we use that all kittens are Bicolours ?

We will use a blue and white Van male to see, if all kittens will be bicoloured: BB dd oo SS.

Example 4: How can we get Vans (homozygous SS) ?

As you have seen in the examples before, if one parent is solid (without white) we only can get Bicolours (heterozygous Ss). Therefore we will use a black and white bicoloured female with a blue and white bicoloured male, to see if we can get Van kittens.
Our male brings us the following genetic background: BB dd oo Ss. Our female brings: BB D- oo Ss.

If you want to know which Bicolours are possible, then klick here.