Shirley Reid, of Timaru, asks :-

Why do cats have litters with so many different colours?

Hugh Blair, a Geneticist at Massey University's Institute of Veterinary Animal and Biomedical Sciences, responded.

The genetics of coat colour in cats is complex, so the question is best answered with a few examples that show this complexity.

A queen can generate many different colours and patterns in her offspring for several reasons, one of which being that she may have mated with multiple toms, a common occurrence when toms are available, and so the kittens may actually have different fathers. Also, not all aspects of coat colours and patterns are under genetic control. Even clones which have the same genetic material can 'look' different. There are many different genes that control coat colours and patterns which allow a wide range of colours and patterns to be generated from one mating. Current estimates are that there are over 400 genes involved!

A consideration of just six of these genes helps explain some of the variation. The agouti (A) gene controls the distribution of colour over the body (patterns), the distribution of colour along each individual fibre and whether the base pigment will be black or red. The A gene allows for solid colours (such as all black) or patterned fibres such as ticking. The Brown (B) gene controls whether the pigmentation will be black, chocolate or cinnamon. The albino (C) gene controls whether the animal can produce pigment or not. An albino cat will show no pigmentation at all while a seal point will only show colour at the ends of its paws, nose and ears. The dilution (D) gene controls whether red is diluted to cream or black to grey or chocolate to lilac. The orange (O) gene controls red and black pigmentation. The tabby (T) gene also controls the distribution of pigmentation including tiger-type stripes, leopard-type spots and the Abyssinian Tabby. These genes all interact to give a cat its unique colour and pattern. Sometimes one gene over-rides another gene, sometimes they mix together to give new colours and patterns.

If a queen and a tom carry the same information at each of the 6 genes mentioned above, their kittens will show little colour variation. This is what happens with purebreeding. However, where the queen and tom carry different information at even just some of these 6 genes, the litter colours can be quite varied.