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 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
1) All cats are tabby. The Tabby gene has 3 main multiple alleles:
T - mackerel, wild type, striped tabby coat pattern
- Abyssinian coat pattern, dominant, typical tabby markings restricted to the
head and face.
- 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
(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
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
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