FUNDAMENTAL BASIC GENETICS
for breeding Abys & Somalis

first published in THE ABYSSINIAN, Journal of the Abyssinian Cat Club of Australasia Inc., June, 1998

Despite appearances our domestic cats are more alike than they are different. Under normal circumstances, all cats have 19 pairs of chromosomes in somatic cells, with each pair member originally derived from each parent. These structures are primarily made up of DNA and carry the basic units of heredity - genes. The chromosome pairs tend to be identical in shape and size but the composition can vary among themselves. The location of all the genes carried on chromosomes is identical for all breeds of cat regardless of what we see as a result of gene expression. All cats are tabby and are either black or red in colour. Variations and breeds are derived through the actions of particular genes.

Genes can exist in various alternative forms called alleles. In genetic notation it is customary to denote a dominant allele by a capital letter and lower case to denote a recessive allele. A homozygous state for a particular gene is where each pair member for that gene is identical, being either dominant or recessive. A heterozygous state is where each pair member is different - the dominant form of the gene being expressed. Genotype is the actual genetic makeup of an animal whereas phenotype is the appearance resulting from that genotype.

Many of the characteristics that we see in our cats are the result of several genes interacting on the same feature e.g. body type and intensity of colour. Many of these characteristics show a great deal of phenotypic variation among animals which is due to the effect of polygenes. For cats, body conformation falls into two basic categories - one being the more heavy set, cobby type such as British Shorthaired Cat and the other the longer finer type of the Foreign Shorthair such as our Abys and Somalis. The variation within these categories is the result of gene interactions and environment. Intensity of coat colour is another feature under the influence of several genes which are collectively called rufous polygenes.

The number of polygenes for a particular feature is the same for all cats. The variation arises due to different numbers of these polygenes being activated. These genes tend to have an additive effect. The more of these genes 'switched on' the greater the intensity of colour.

Coat pattern and colour tend to be under the influence of single genes, generally with a simple dominant/recessive interaction. From a breeders point of view it is these genes which can be recognised, selected for or against, and used as an aid in predicting likely outcomes of matings.

For our Abyssinians and Somalis there are several main genes of special interest:

1) All cats are tabby. The Tabby gene has 3 main multiple alleles:

  • T - mackerel, wild type, striped tabby coat pattern
  • T a - Abyssinian coat pattern, dominant, typical tabby markings restricted to the head and face.
  • t b - blotched coat pattern

2) Agouti gene (A-) causes alternation of the rate of pigment production in the hair shaft which results in banding (basic black and yellow). With Non-Agouti (aa) there is no banding in the hair shafts and this results in 'self' coloured cats.

3) Black pigment (B-) gene gives us our black ticked cats. There are two other alleles in the pigment series:

  • b (brown) - gives a dark brown/chocolate pigment
  • b l (light-brown) - gives light brown/cinnamon pigment

Red cats have a sex-linked gene (O) which gives their orange pigment. This gene is carried on the X chromosome. Our Abyssinians and Somalis (NSW CFA) have genes for black (B-) and light-brown (b l -)only.

4) The gene for dense pigmentation (D-) maintains the colour produced by the black and light-brown genes. This form produces our Tawny and Silver from the black gene (B-), and Cinnamon and Cinnamon Silver from the light-brown gene (b l -).

The recessive form of 'Dense' is the 'Dilute' gene. This gene has an effect on the melanin in the hair shafts. The end result is that black pigment appears blue, light-brown produces fawn, and brown pigment produces lilac.

5) The Inhibitor gene (I-) suppresses the ground colour in the hair shafts, which gives a silver/white undercoat - there is no effect of the ticking colour. The recessive form (ii) has no suppression of pigment e.g. Tawny.

6) The White Spotting gene is a dominant gene (produces white patches) and is an undesirable gene for our Abyssinians and Somalis. This is the source of features such as white lockets.

7) The gene for short hair (L) is dominant over longhair(l). This gene is also subject to effects of polygenes and, of course, selection by breeders to maintain divisions such as 'semi-longhaired' and 'longhaired' cats.

Recessive genes can be carried for several generations without being detected or even suspected. By maintaining accurate records of offspring and the history of reproduction performance of relatives, and perhaps, doing appropriate test matings, we will discover what lies at the genetic heart of our cats' appearances.


Fiona Mangan     June, 1998


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