But I've heard that white cats might be deaf.
How can it be possible to allow breeding with white cats ?

You are partly right. There is a theory that white cats might be deaf. White cats with blue eyes are most likely to inherit deafness. Deafness will be found on that ear where the blue eye is placed, that means also odd eyed white cats might be deaf, unilateral. The probability is quite high with white cats with blues eyes, more than 25%.

"After all that it should be forbidden to breed with white cats !" Why ?

Breeding cats is an artificial way of reproducing cats, as it is controlled by humans and we don't allow our cats to reproduce themselves as often as it would be possible and our cats would like to do so.
Therefore why should we not control our breeding programs by strict selective breeding that we don't produce deaf white cats ?
By the way the white colour is not an artificial colour, not a man-made colour, you'll find a lot of white mammals in nature. Do we all distinguish them because they are white ?

You see, this question is not as simple to be solved as it appears to be. This question wether to breed with white cats or not has a lot more impacts, this question is of the same quality as one could ask
"Why is it permitted to have cars ?"

May be, You've got a small idea that apodictic rules and taboos don't bring anything for the white cats.

"Don'ts and No's" will not stop people from breeding white cats and, even worse will increase the amount of deaf white cats.

Information, carefully planned guidelines and selective breeding programs make it possible only to have white cats which all do hear.

If you've read the little aphorism carefully, the solution of this crucial problem, named deafness, are the CARS.

You remember, in the beginning we wrote that there is one theory that gene W together with blue eyes is the source for the inheritance of deafness. That's one theory.
Another one is that gene S - you remember, the gene for piebald spotting, called bicolour - 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, f.e. think about the Hungarian Shepherd or the Akita inu, which both are bicoloured.

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.

Concerning the first theory that gene W is involved in the inheritance of deafness there are existing a lot of statistical data. But's worthwhile to start investigations on bicoloured cats and collect statistical data, too.

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

As we've discussed gene W covers all colours - is called a mimic gene, we'll make some small examples to see what we can get.
It's irrelevant if the male or the female is white. Therefore we will assume that the female is white.

Example 1

Our male might be blue tabby: A- B- dd ii oo ss mcmc ww
Note that we will not write the pairs ii, oo and ss in the following table as they are not relevant and our combinations would get too long and difficult to read.
Our female is the white one: W-
That's all what we know about our female.
You breed this two cats and get the following litter:

Let's make the following assumption: You have got blue and red kitten out of this mating.
Then you can make the following conclusions about your female that she must carry at least the following gene pairs:

• About gene B you can't still say anything. It depends if there are chocolate/lilac ancestors in the pedigree of your female. Your female could have bb, Bb or BB.
  If you get a chocolate or lilac kitten, you know immediately that your male must carry Bb and your female must have at least one gene b. But your female still can carry bb or Bb, you have to look on her ancestors.
• About gene C you can't say anything, it depends if your female has ancestors which show a siamese/burmese pattern.
  If you get a colourpoint kitten f.e., then your male must carry Cc^s. Remember, both of the parent must carry at least one gene c^s that their kitten can get the gen combination c^sc^s. About your female you only can say that she must carry at least one gene c^s, but she still can carry c^sc^b, c^sc^s, c^sc^a or c^sc.
• Your female must carry Dd because of the blue kitten. She also must be heterozygous for dilution, otherwise you would have got only cream kitten and not a red one.
• About gene I you can't say anything, it's the same as with gene B, it depends on the ancestors of your cat. Your female could carry either Ii or ii.
  Your male carries ii, that 's for sure as he is blue tabby and not blue silver tabby. Only one gene I must be present to see the silver already in the phenotype. Due to the fact that in this litter there is no silver kitten you can't draw any conclusions.
  Only if there is a silver kitten in this litter, you know that your female must carry at least one gene I.
• The female can carry OO or Oo. It depends on her ancestors. Besides the red kitten must be little boys. You can only get red girls if both of the parent carry at least one gene O, as our male is blue tabby, he carries oo and therefore can't produce red girls.
• About gene S you can't say anything, your female could carry Ss or ss, it depends on her ancestors.
• Concerning "tabby", you can't say if your female carries gene A or gene a. To show the tabby pattern in the phenotype only one gene A is already enough, if you have got a kitten with a tabby pattern gene A could have come also from the male. Every cat carries a pair of the tabby genes Mc or mc, in which combination, you can only decide on behalf of the tabby pattern.

This example demonstrates how you can figure out the genetic background of your breeding cats on behalf of their litter what you get from them. And so, step by step (litter by litter) you can draw conclusions about the genetic background of your cats you use for breeding.
This example also demonstrates the mimic character of gene W, gene W covers every colour, turns every colour to white.

Example 2

Let's stay with the litter of Example 1. You should watch them carefully.
Mostly white kitten have a coloured patch on the top of their head which disappears when the kitten grow up. If you are lucky to find out of which colour this patch is you have come a step further. This coloured patch tells you something about the genetic background of this white kitten:

• If the patch is black, the kitten must carry at least one gene B and at least one gene D.
• If the patch is blue, the kitten must carry dd and at least one gene B.
• If the patch is red, the kitten must carry at least one gene B, one gene D and one gene O - as our male was blue tabby, the kitten can carry OY or Oo.
• If the patch is cream, the kitten must carry at least one gene B, dd and one gene O - as our male was blue tabby, the kitten can carry OY or Oo.
• If the patch is chocolate, the kitten must have one of the following gene combinations, bb or bb^l; the kitten also must carry at least one gene D.
• If the patch is lilac, the kitten must carry either bb or bb^l, but it also carries dd.
• If the patch is tortie, the kitten must carry Oo.