College of Cat Genetics: Part XIV
by Patricia Turner
Study Unit 14
Programmes of Matings
The cat breeder has a number of considerations to bear in mind when arranging programmes of matings. He may be seeking to "improve" type with reference to a cat fancy standard of points for the breed concerned, he may be attempting to eliminate a characteristic he considers undesirable or he may be hoping to transfer a quality of colour from one breed to another.
Artificial and Natural Selection
There are cat lovers who maintain that "natural" breeding is best and that "tinkering about with genetics" results only in freaks. Even if agreement could be reached over the definition of "freak", it is doubtful that such a hypothesis could be effectively proved in an age where the domestic cat population is already largely determined by man's selection. The very words "domestic cat" imply this selection. In fact, were man to have had no hand at all in the shaping of contemporary cat populations then no doubt most of the cats in Europe would be rangy, wild, short-haired tabby creatues inhabiting the woods while those in warmer more humid climates would be correspondingly darker in colour.
While domestication by man has not been the cause of the many variants, there is no doubt that it is responsible for providing the opportunity for the variants to spread. Long before William Bateson advised animal breeders to "treasure your expectations", cat lovers had begun to do so by favouring certain mutants and selecting for them. An extremely good example of the effect of man's selection is that of the blotched tabby, already mentioned as being the result of a recessive mutant. In fact, tabby pattern (as distinct from agouti which gives it expression) has three alleles and of the three "blotched" is the most recessive. This pattern, often described in the cat fancy as marbled is thought to have mutated much later than the Abyssinian tabby pattern as seen in Felis chaus and the striped (or mackerel) tabby pattern as seen in Felis lybica. However, it is gradually displacing the other two patterns in non-pedigree cat populations. Worldwide gene surveys have shown that it is gradually spreading out from urban centres in Europe, and the inference is obvious. When left to themselves even domestic cats operate no particular colour bar -- the average tom cat is happy to sire kittens to any queen of any colour or shape. The forces of mutation, natural selection, and gene-flow between semi-isolated cat populations would not account for the diversity, allocation and frequency of certain colours and patterns without artificial selection by man playing its part.
An interesting report by Roy Robinson and Maureen Silson, England, shows unexpectedly large discrepancy between the numbers of red cats observed in areas of Southern England and the number that would be expected to occur. Again one explanation they considered is a human bias towards keeping red cats in preference to others.
Evolution of Pedigree Breeds
The selection practised by the pedigree cat breeder is really only an extension of the selection practised by the average cat lover over the centuries. Selection has led to the evolution of the pedigree cat breeds and the breed names chosen, although in some cases reflecting the place of origin (or supposed origin) are basically descriptions for combinations of qualities of coat, colour, pattern, shape, build and general character. It is selective breeding for particular characteristics practised by serious cat fanciers that has resulted in the evolution of the individual breeds.
The production of each breed has involved "shuffling" of genes that have at some time in history mutated from the normal or wild type. In this context the use of the word "normal" does NOT infer that the mutated gene is in any way "abnormal" -- it is a general term for the alternative to the mutation. While in the cat fancy the age of a mutation usually adds to its "respectability", it must be remembered that at some stage in history even the best known and oldest mutants must have been new.
Of course there are some mutants that are definitely harmful although these usually affect characteristics other than those involved in the evolution of breeds and should thus be the concern of all cat lovers. An example of this sort of mutant is that for congenital hydrocephalus recently reported in Siamese but likely to occur in any breed. Other mutants may be regarded as undesirable by some while not strictly speaking harmful. Such a mutant is polydactyly and which, in the cat fancy, generally is selected against, abounds in such frequency in certain parts of the world that artificial selection in its favour must almost certainly have been involved. There are some mutant genes with pleitropic effects as explained earlier in this series, although pleitropic effects need not necessarily be harmful.
Some mutants, such as that for dilution, already discussed, are recessive; others such as white coat are dominant. Sometimes a new mutant may produce an effect considered attractive by cat breeders who then, by a planned programme of matings, find the method of inheritance and then tests its viability and increase its frequency. By such means new breeds may be produced. The Cornish, Devon and German Rex mutants are good examples.
Other breeds are the result of chance or considered combinations of genes other than those previously found in association. Breeds such as these are the Siamese "32's" (Tabby Point, Red Point, Tortie Point, Any Other Dilution); the Havanas; while those varieties such as Havana dilutes (Foreign Lilac); Foreign White; Chocolate British SH and Persians; Red and Cream Burmese, etc., represent breeds in the making.
Breeds with programmes for their production planned in advance are often called "man-made", although "man designed" would probably be more accurate since they are made with the materials (genes) already present in the cat populations.
None of the programmes for their production represent anything more than considered attempts either to combine for the first time, or to reproduce a combination already seen as a result of chance matings, alleles at different loci.
Study Unit 15 will discuss designed breeds.