A Word About Genetics - Recessive Gene Inheritance

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A Word About Genetics

Before this report can concern itself with the Somali's origins a capsule review of certain genetic facts need to be reiterated.

Short-hair, when pure and mated to its like will produce short-hairs (except in the case of mutations). Long-hairs likewise will produce long-hairs. The long-hair gene is recessive and therefore can easily be masked by the dominant short-hair gene. Thus a feline that may have the outward appearance (phenotype) of being genetically homozygous may actually be harboring the recessive long-hair trait. This heterozygous (long-hair - short-hair) feline has a fifty - fifty chance of passing the long-hair gene on to its offspring.

Because the inheritance of coat length is multifactorial rather than of a Mendalian character, polygenes are acting upon the main genes producing various coat lengths within the breeds.

What happens when heterozygous felines (long-hair carriers) are mated to homozygous short-hair, homozygous long-hairs or other heterozygous cats can best be expressed by the following illustrations:

NOTE: In order to clarify the subject of genetics for the novice some notes have been added here in this 1999 edition.

Coat length is an inherited factor from both parents. Offspring inherit one gene for coat length from each parent. Thus if the offspring inherits one short-hair gene from one parent and a long-hair gene from the other parent the kitten will appear (phenotype) to be shorthair but its genetic makeup (genotype) will be mixed.

S = short-hair gene
L = Long-hair gene

SS = Pure short-hair (one 'S' gene inherited from each parent). Its appearance and genetic makeup (genotype) is pure and it makes it impossible to pass on the long-hair gene.

LL = Pure long-hair (one 'L' gene from each parent). This feline is a long-hair in both genotype and phenotype. All long-haired cats are genetically 'LL'.

SL = Mixed gene carrier (one 'S' gene inherited from one parent and one 'L' gene inherited from the other parent). This cat outwardly appears to be a short-hair but secretly carries the recessive long-hair gene in its genetic makeup.

The various combinations of these matings will produce litters in the following proportions. Bear in mind, however, that nature does not follow mathematical models and results will vary. (translation - in the real world, breeders working to produce long-hairs will get litter after litter of only short-haired kittens while the breeder who despises the long-hairs will be blessed with nothing but!)

Homozygous short-hair (SS) mated to homozygous short-hair (SS) will only produce offspring that are genetically pure (SS) and will appear only as short-hairs.

Homozygous long-hair (LL) mated to homozygous long-hair (LL) will only produce offspring genetically pure (LL) and will only appear as long-hairs.

The problem of knowing what type of coat length a cat will produce in its offspring occurs when that cat is the product of a homozygous short-hair (SS) mated to an heterozygous short-hair (SL). Outwardly that feline will appear to be a short-hair because the short-hair gene is dominant but it may harbor the recessive long-hair gene it inherited.

Homozygous short-hair (SS) mated to heterozygous short-hair (SL) will produce kittens that all appear to be short-hair, having inherited at least one short-hair gene from the homozygous parent (SS) but because the other parent is hiding the long-hair gene there is a fifty per cent chance that the recessive long-hair gene will be passed on to its offspring.

Heterozygous short-hair (SL) mated to another heterozygous short-hair (SL) will produce a litter consisting of 75% which will appear to be short-hair and 25% that will be long-hair. Of the short-hair kittens one in three will be a homozygous short-hair (SS),the other two will carry the long-hair gene (SL).