Can breeding from black Maus improve the contrast and clarity of bronzes?
By Melissa Bateson.
Some breeders hold the view that black Egyptian Maus can successfully be used in a breeding programme to clean up the contrast in ticky cats. I have never believed this myth, and my aim in this article is to explain why.
A black mau is gentically only ONE GENE different from a bronze: it is a non-agouti cat (genetically aa) whereas a bronze must have at least one copy of the dominant agouti gene (i.e. it must be Aa or AA). Black maus can come from any breeding in which both parents have a copy of the a gene (i.e. both parents must be either Aa or aa), one example is the breeding of two Aa bronzes (Aa x Aa) which will produce on average one black kitten in four.
If you breed a bronze mau from one black parent then it will inevitably be of the heterozygous Aa genotype, because it can only inherit an a gene from the black parent; the A has to come from its bronze parent.
The important thing to understand is that black Maus will carry ALL of same rufous polygenes and the genes that control the contrast and pattern that you see expressed in a bronze, you just can see the effects of these genes because they are masked by the dark colour (you can sometimes see a ghost tabby pattern in young black kittens). The parents of a black Mau are your best guide to the genes it will carry. A black mau from two highly rufous parents is likely to produce highly rufous bronze offspring, and a black Mau from very ticky parents is likely to produce very ticky bronze offspring, because it will have inherited the genes for these traits from its parents.
There are only two ways in which breeding from a black Mau could lead to improved clarity or contrast in the offspring. The first is if the black Mau comes from very clear contrasty parents, in which case it is likely to carry the genes for clarity and contrast and pass them onto its offspring. The second is if heterozygous Aa bronzes actually have better clarity and contrast than AA bronzes, since all the bronze off spring of a black will be Aa. If this was the case it would have to imply that the A gene is not fully dominant because, by definition, a dominant gene has the same effects on the phenotype (what the cat looks like) when there are one or two copies present. I can not find any evidence to suggest that the A gene is not fully dominant, therefore, all else being equal, an Aa cats should look identical to an AA cat.
The conclusion is that there is nothing to be gained from breeding from a black Mau. It is in effect like picking a breeding cat with your eyes closed, which is not a very sensible strategy in a breed where more than 50% of the points are based on colour, contrast and pattern! Indeed breeding from blacks will just ensure that all the bronze offspring are of the Aa genotype thus making it more likely that you will produce more blacks in the future.
I think the idea that breeding from black Maus improves clarity and contrast comes from a misunderstanding of genetics: if you don't know how genetics works it might seem plausible that if you breed from a black cat then the bronze kittens might be blacker, but this is just not the way it works. The myth has also probably been propagated by a few cases where breeding from blacks has apparently worked just by coincidence. Being very cynical I think that the myth that black maus leads to improved contrast is sometimes used as a ploy by breeders trying to find homes for black kittens.
My advice would be not to breed from a black unless the lines it carries are extremely important to you, or possibly if it is exceptional in every other respect. You would be far better off breeding from your best bronzes where you can actually see the effects of the genes for colour, contrast and pattern carried by the cat.