BASIC CAT GENETICS.

Dr David Richardson (M.B.. B.S. hons) RAGAJAC CATTERY

Jacqui Richardson Email ragajac@bigfoot.com

Fax 02 96531385

In the 1860’s an Austrian Monk called Gregor Johann Mendel experimented with pea plants to try and determine a basis for inherited characteristics. He was wonderfully successful though his work remained undiscovered until early this century.

Mendel’s work provides a scientific basis for breeding all biological species, both plant and animal.

Gaining an understanding of Mendelian genetics as applied to the cat, provides a scientific basis for breeding programs and takes a lot of the guesswork out of our hobby.

At Ragajac Cattery our interest is breeding the traditional Ragdoll and we find Mendelian genetics can be applied to many of the characteristics of this breed.

In this article we will discuss the genetics which cause the main colours of the Ragdoll (and all other Himalayan patterned cats).

Mendel discovered that some genes were dominant over others. Each animal has a genetic makeup which is called the genotype causing a specific characteristic appearance which is called the phenotype. For example, a seal point phenotype Ragdoll can be caused by a number of different genotypes.

Genes are given the symbols of letters using an upper case letter for a dominant gene and a lower case letter for a recessive gene.

For each characteristic there are two genes, one from each parent, and these genes may be the same or different. A cat carrying two identical genes whether they are dominant or recessive is called homozygous ("homo" means the same, as in homosexual). A cat carrying a combination of a dominant and recessive gene is called heterozygous ("hetero" means different as in heterosexual).

To complicate matters a little further, the common Ragdoll cat colours (seal, blue, chocolate, lilac) are caused by a combination of two genes. Traditionally in the cat, the gene "B" is for black, and the gene "D" is for undiluted colour. In the Ragdoll, the presence of a "B" combined with a "D" gives not a black colour but the deep brown seal colour that we all know. Blue and chocolate colours result from the impact of diluting genes on the seal. The presence of at least one "B" but with two recessive "d" dilute genes gives the blue colour. The presence of least one "D" but with two recessive "b" dilute genes gives the chocolate colour. A combination of "b" and "d" with no dominant genes gives a lilac colouring (Double recessive).

Remember for each characteristic one half of the gene comes from each parent. So a seal point cat can be any of the following combinations:

1. BB DD Homozygous seal.

2. BB Dd Heterozygous seal. Most breeders know this as carrying blue dilute.

3. Bb DD Heterozygous seal. Carrying choc dilute.

4. Bb Dd Heterozygous seal. Carrying both dilutes.

To reiterate, all of the above will be seal point cats phenotypically, but as you can see they are quite different genotypically.

Now the beauty of all this mumbo jumbo is that if we know the genotype of our cats, we can predict accurately what phenotypes their offspring may be. Thus if we have two homozygous seals the only possibility for offspring is more homozygous seals (100%). BB DD x BB DD = BB DD. However, at the other end of the scale, two heterozygous seals (Bb Dd), can produce seals, blues, chocolates and there is even a one in sixteen chance of lilac!

This is illustrated by the following diagram:

The diagram shows that if you are lucky enough to mate two seal cats carrying both dilutes , the resulting kittens have a 9/16 chance of being seal, 3/16 chance of being blue, 3/16 chance of being chocolate and a 1/16 chance of being lilac.

More Genetics.....See also our links page