When I first started breeding Maus in 1996 cat colour genetics were a complete mystery to me. I asked some other breeders for explanations and was told rules of the type 'smoke x smoke = smoke and black', 'bronze x bronze = bronze and black' and 'silver x silver = anything'. Although these rules are correct, it turns out that they are too general to be very useful. I wanted to breed silvers, but although my first two litters were from silver to silver breedings I got a complete rainbow of kittens: a total of four silvers, two bronzes, a smoke and two blacks.....Why was I being so unlucky when I saw other breeders having litter after litter of silvers? Finally I began to understand when my breeder friend Melanie Morgan sent me an article on Mau colour genetics written by Kerry Conway of Kaakhamit cattery. I realized that with a little detective work I could have much greater control of the colours of my future kittens. I think Melanie and I spent about two hours on the phone excitedly trying to work out the genetics of all of our cats. It has been well worth the effort. In 2001 I had three litters of kittens, one of two, one of six and one eight, ALL silvers ! My intention in the article is to introduce breeders to the genetics of the four basic mau colours, and provide some simple rules for predicting the outcomes of different matings. I have not included the blues or classic tabbies here because they are very rare and hugely increase the number of possibilities that need to be considered.
The equivalent colour is also found in breeds such as the British Shorthair, the Oriental and the Ocicat, but note that the silver Mau is genetically completely different from the snow Bengal, whose pale colour is produced by the Siamese or Burmese colour restriction gene, not the silver gene. The color and pattern of the silver Mau are produced by the addition of just two dominant alleles (variants of a gene) to the solid black Mau: the inhibitor allele, I, and the agouti allele, A. The dominant inhibitor allele, as its name suggests, inhibits the deposition of brown color in the hairs and is thus responsible for the silver color. The dominant agouti allele causes pigment in the hairs to be deposited in bands along the hair producing the effect known as ticking. Presence of the agouti allele, A, is necessary for the tabby pattern to be clearly seen. A Mau with AT LEAST ONE I allele AND AT LEAST ONE A allele will be a silver. Therefore, since each cat has two copies of each gene, one inherited from the dam and one from the sire, there are four different types of silver Mau (known as genotypes). A cat is referred to as homozygous for a particular gene if both alleles are the same, and heterozygous if they are different. Hence the four genotypes of silver Mau can be described as follows:
There is some debate about whether or not these four different genotypes have different physical appearances (known as phenotypes) associated with them. There is some evidence from other breeds (e.g. Persians) that although the I allele is dominant, its effects are somewhat additive. Thus a cat with two copies of the I allele might show greater inhibition of color than a cat with just one. We might therefore expect II silvers to be less tarnished (i.e. have less yellow or brown colouration) than their Ii littermates. This hypothesis remains to be tested, however based on my own limited observations it does seem to be the case that silvers with tarnish are more likely to carry bronze (i.e. have the Ii genotype) than their cleaner coloured litter mates.
Aside from the possibility of phenotypic differences between the four types of silvers, the genotype of a cat has important implications for breeding. By the judicious pairing of cats of known genotype it is possible to control the number of colours that can occur in the offspring. The colour table I have created shows the proportions of different colors that will arise on average from all the possible pairings of Mau genotypes. To use the table all you need to do is (1) determine the genotype of your cat, (2) determine the genotype of the cat it will be mated to, and (3) read off the average percentages of different colours from the appropriate cell of the table. Neither the agouti nor the inhibitor genes are sex-linked, thus it is not relevant which cat is the dam and which the sire. Bear in mind that unless the percentage given is 100%, in which case you can predict exactly what you will get, these percentages represent the AVERAGES ONLY, and you are unlikely to get exactly the given percentage in any single litter. Although, if the mating is repeated many times, the proportions of kittens of different colours produced should approach the percentages in the table.
So now you are probably asking, 'How do I determine the genotype of my cat?' Here are a few simple rules for silvers. Similar rules for bronzes and smokes follow below.
First look at the kittens your cat has produced. This is the most reliable method of determining a cats genotype.
Second, look at your cat's pedigree. This is less reliable because it depends on the pedigree being correct.
Third, look at your cat. This method is not proven to be reliable at this stage.
Similar rules to those outlined above can also be applied to determine the genotype of bronzes and smokes, and will be outlined in detail in the following sections.
Brown tabbies are known in may breeds such as for example the British Shorthair, the Ocicat, and the Oriental, however, the warmer bronze colour of the Mau is only seen in the brown Bengals and the usual Abyssinians. The bronze color is achieved by the addition of the dominant agouti allele, A, to the solid black Mau; thus a bronze is a Mau with AT LEAST ONE A allele. As in the silvers, the agouti gene causes ticking on the hairs revealing the spotted tabby pattern. Bronzes lack the dominant inhibitor allele found in the silvers and smokes.
There are two distinct bronze genotypes determined by whether the cat has one or two copies of the dominant agouti allele:
The warmness of the coat colour is determined by the presence of what are known as 'rufous polygenes'. As their name suggests there are many of these genes, and the more a bronze Mau has the warmer its colour will be. The usual Abyssinian is an example of another brown tabby (in this case of the ticked rather than the spotted pattern) that has been selected for a large number of rufous polygenes. The practice of breeding bronze to bronze generation after generation (known as 'colour breeding') paired with the selection of the warmest cats from each generation causes the accumulation of rufous polygenes within a line that is necessary to produce really warm bronzes. Breeding programs for warm bronzes and clean silvers probably cannot be successfully combined, since the rufous polygenes necessary for warm bronzes will result in tarnished silvers.
Determining the genotype of a bronze: First look at the kittens your cat has produced previously
Second, look at your cat's pedigree:
that has been selected to have very prominent ghost markings. A smoke Mau has AT LEAST ONE inhibitor, I, allele, but lacks the agouti, A, allele. Thus despite its markings the smoke is not a tabby (i.e. agouti) cat. Egyptian Maus are unusual in having a patterned smoke. There is no equivalent of the smoke Mau in other breeds since although black smoke exists as a colour in many breeds, these other smokes are preferred to show no tabby markings.
Smoke Maus are often used in silver breeding programs. Mixing smokes and silvers is not fraught with the same problems as mixing warm bronzes and silvers because with both the smokes and silvers it is desirable to select for as few of the tarnishing rufous polygenes as possible. Thus silvers and smokes can be interbred without detriment to either colour. On the contrary, some breeders maintain that smokes are actually useful for producing silvers with a high level of contrast between the spots and ground color. It is certainly the case, that some of the most black and white silvers I have seen have been produced from smoke to silver matings, and I have been particularly intrigued by the explanation for this phenomenon. The obvious explanation is that silvers carrying smoke (i.e. those with AA genotypes) have better contrast than silvers not carrying smoke (i.e. those with AA genotypes). This would imply that the agouti gene is additive in its effects with a single A producing a cat with higher contrast than a cat with two AAs. However, I have been able to find no evidence from other breeds that this is the case: the agouti gene is believed to have a simple dominant effect such that AA cats are visually indistinguishable from AA cats. My preferred explanation for the phenomenon is as follows. I believe that the smokes retained for breeding probably have much better contrast relative to the pool of all smokes produced than the average silver breeding cat does relative to the pool of all silvers, and it is this that leads to the better contrast observed in the silver offspring of smokes. Breeders are selecting smokes more on the basis of contrast than they are silvers because a smoke Mau has to have exceptional contrast in order for the spots to be visible, whereas in a silver a lesser degree of contrast may be tolerated in a breeding or show cat if it has other desirable traits. Also, the dark color of the smoke may mask traits that would cause a silver to be rejected as a breeding cat, for instance, tarnish will not be visible on a smoke, and even some pattern flaws may not be so obvious. For these reasons I believe that contrast is a more dominant criterion in the selection of smokes for breeding than it is in the selection of silvers. If these arguments are correct, then the implication is that it is not necessary to breed to smokes to get good contrast; the same effects could be achieved by breeding from silvers with the highest contrast.
As with the bronzes, there are two distinct smoke genotypes determined by whether the cat has one or two copies of the dominant inhibitor allele:
Determining the genotype of a smoke:
First look at the kittens your cat has produced previously:
Second, look at your cat's pedigree:
with the black masking the spotted tabby pattern. There is only one type of black Mau, aaii, and it is the most recessive of the many Mau genotypes (excluding the blues). The fixed genotype of the black Mau, aaii, gives it specific uses in a breeding program. Blacks can be used to perform test crosses to reveal the genotypes of other cats. For example, if a silver is bred to a black and produces only silver kittens time after time, then the chances are very good that the genotype of this silver is AAII.
The down side of using a black in a breeding program is that it is equivalent to choosing a breeding cat with your eyes closed! Given the importance attributed to colour, pattern and contrast in the Mau standard, using a black Mau in a breeding program is not something to be undertaken without some thought. The black masks not only the pattern, making it hard to see whether the cat has any pattern faults and how good its contrast is, but also the rufous polygenes, making it impossible to tell how tarnished it is. It's important to remember that just because you can't see the pattern, contrast and tarnish it does not mean that there are not genes for these traits present; they are there, you just can't see their consequences. Of course the black Mau's parents can be used to get some idea about the pattern and contrast genes it is carrying and the number of rufous polygenes it is likely to have. A second problem of breeding from blacks is that the probability of producing black kittens is greatly increased (see the colour table for details). In general it is not advisable to breed from a black Mau unless it comes from irreplaceable lines or it has absolutely outstanding health, temperament, type and eye colour.