PROS AND CONS OF INBREEDING

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*http://www.messybeast.com/inbreed.htm*

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*PROS AND CONS OF INBREEDING*

*Copyright 1996, 2001, 2003 Sarah Hartwell*

 

Inbreeding is the mating together of closely related cats, for example

mother/son, father/daughter, sibling/sibling matings and

half-sibling/half-sibling. It is the pairing of animals which are more

closely related than the average population. For breeders, it is a useful

way of fixing traits in a breed - the pedigrees of some exhibition cats show

that many of their forebears are closely related. For example, the name of

Fan Tee Cee (shown in the 1960s and 1970s) appeared in more and more Siamese

pedigrees, sometimes several times in a single pedigree, as breeders were

anxious to make their lines more typey. Superb specimens are always much

sought after for stud services or offspring (unless they have already been

neutered; cloning may solve that problem in the future) having won the

approval of show judges.

 

To produce cats which closely meet the breed standard, breeders commonly

mate together animals which are related and which share desirable

characteristics. Over time, sometimes only one or two generations, those

characteristics will become homozygous (genetically uniform) and all

offspring of the inbred animal will inherit the genes for those

characteristics (breed true). Breeders can predict how the offspring will

look. " Line-breeding " is not a term used by geneticists, but comes from

livestock husbandry. It indicates milder forms of inbreeding. Line-breeding

is still a form of inbreeding i.e. breeding within a family line and

includes cousin/cousin, aunt/nephew, niece/uncle and grandparent/grandchild.

The difference between line-breeding and inbreeding may be defined

differently for different species of animals and even for different breeds

within the same species. It is complicated by the fact that a cat's

half-brother might also be her father!

 

However, inbreeding holds potential problems. The limited gene-pool caused

by continued inbreeding means that deleterious genes become widespread and

the breed loses vigour. Laboratory animal suppliers depend on this to create

uniform strains of animal which are immuno-depressed or breed true for a

particular disorder e.g. epilepsy. Such animals are so inbred as to be

genetically identical (clones!), a situation normally only seen in identical

twins. Similarly, a controlled amount of inbreeding can be used to fix

desirable traits in farm livestock e.g. milk yield, lean/fat ratios, rate of

growth etc. In human terms, inbreeding is considered incest; cats do not

have incest taboos.

 

Outcrossing is when the two parents are totally unrelated. In pedigree

animals, this often means where a common ancestor does not occur behind

either parent within a four or five generation pedigree. In animals with a

small foundation gene pool, this condition is difficult to meet.

 

First I will define some terms used by animal breeders. In general I've

avoided specialist terms, but you will meet these terms outside of this

article.

 

*Homozygous* means having inherited the same " gene " for a particular trait

from both parent e.g. for fur length. Barring random mutation, 100% of the

offspring of a homozygous individual will inherit that gene. Inbreeding

increases homozygosity by " fixing " a particular trait. Purebred animals

display a high degree of homozygosity compared to mixed breeds and

random-bred animals. The idea of purebred animals is that they should " breed

true " . When one purebred is mated with another of the same breed, the

offspring will have uniform characteristics and will resemble the parents.

 

*Heterozygous* means having inherited a different gene for a particular

trait from each parent. For example one gene of long fur (recessive) and one

gene for short fur (dominant). 50% of a heterozygous individual's offspring

will inherit one form and 50% will inherit the other. Carefully controlled

" out-crossing " increases heterozygosity for selected traits by introducing

new genes into the hybrid offspring.

 

*Heterosis* is the scientific term for hybrid vigour. It is possible that

there are " bad " genes which produce less vigourous individuals when in the

homozygous state because good genes have been bred out along with the

undesirable characteristics; theoretically the bad genes could be bred out,

but in practice this doesn't seem to happen. The other theory is simply that

you simply need to have a mixture of two different genes to get the desired

effect as they somehow complement each other; highly inbred animals lack

this diversity and have poorer immune systems.

 

*Sex-linked* refers to a trait which is passed on, or determined by, a

particular gender. In Abyssinian cats there are several versions of the red

colour. One is sex-linked i.e. a male cat only needs one copy of the gene,

but a female needs two copies of the gene to produce the red colour.

 

*Degree of homozygosity* means the number of genes an animal is homozygous

for. If most of its genes are matched pairs it has a high degree of

homozygosity; if most of its genes are mismatched pairs it has a low degree

of homozygosity. An animal can be homozygous for some traits, but

heterozygous for others.

*

 

NATURAL OCCURRANCE OF INBREEDING*

 

This is not to say that inbreeding does not occur naturally. A feral colony

which is isolated from other cats, by geographical or other factors, can

become very inbred especially if a dominant male mates with his sisters,

then with his daughters and grand-daughters. When he is deposed it will most

likely be by his own son or grandson which therefore continues the

inbreeding. The effect of any deleterious genes becomes noticeable in later

generations as the majority of the offspring inherit these genes. Scientists

have discovered that cheetahs, even if living in different areas, are

genetically very similar. Possibly disease or disaster drastically reduced

cheetah numbers in the past creating a genetic bottleneck. All modern day

cheetahs may be descended from a single surviving family unit hence their

genetic uniformity.

 

In the Cheetah, the lack of genetic diversity makes them susceptible to

disease since they lack the ability to resist certain viruses. Extreme

inbreeding affects their reproductive success with small litter sizes and

high mortality rates. Some scientists hope that the appearance of the " King

Cheetah " , characterised by its blotched markings, means that the Cheetah can

develop a healthier gene-pool through mutation (provided man doesn't wipe

them out in the meantime). Mankind has contributed to the loss of diversity

by sport-hunting cheetahs and reducing the number of available mates.

Hunters preferred to shoot unusual specimens (i.e. genetically diverse ones)

for the trophy room and this previously included long-haired " woolly

cheetahs " and grey/blue cheetahs indicating much greater genetic diversity

in the past.

 

Despite the hopes of scientists, some cheetah populations are showing

further signs of inbreeding. Confined to ever-smaller areas such as wildlife

reserves, the populations have become genetically isolated from each other.

In one population there is an increasing frequency of misaligned jaws and

kinked tails. Continued inbreeding will reinforce, or fix, these traits.

Ultimately, they could reduce the cheetah's hunting effectiveness - the

kinked tail will reduce its agility and cornering ability and the misaligned

jaws may not be able to hold onto prey.

 

The wolf was once widespread throughout North American, but many of the

remaining packs are isolated and have become inbred. The

isolation/inbreeding problem has become so acute that conservationists have

taken wolves from one area and introduced them into a another area to

revitalise the gene pool. In some areas, the choice of mates is so reduced

that wolves have resorted to mating with domestic dogs - an extreme form of

outcrossing called hybridization. A similar situation in Scotland where the

Scottish Wildcat mates with domestic cats is threatening to wipe out the

wildcat as domestic cat genes become more widespread. These are two cases

where outcrossing (following, and followed by, inbreeding) may lead to

extinction of a species (analogous to loss of type in domestic breeds).

 

Another animal suffering from the effects of inbreeding is the Giant Panda.

As with the Cheetah, this has led to poor fertility among Pandas and high

infant mortality rates. As Panda populations become more isolated from one

another (due to humans blocking the routes which Pandas once used to move

from one area to another), Pandas have greater difficulty in finding a mate

with a different mix of genes and breed less successfully. It is almost

inevitable that the Giant Panda will become extinct even if cloning

techniques become available since the gene pool is now probably too

impoverished for the species' long term viability. It may, therefore, be

considered that all purebred animals will ultimately become unviable through

inbreeding and that breeders must work carefully to maintain type while

slowing down the detrimental effects of selective breeding.

 

There have been numerous studies into inbreeding and viability. Mandarte

Island, off Vancouver, Canada is so tiny that every single song sparrow can

be ringed, monitored and matings recorded. Researchers know exactly how

inbred each individual is. When severe winter storms wiped out over 90% of

the birds, Lukas Keller of Zurich University, Switzerland found that all

inbred individuals were killed. He defined " inbred " as matings between first

cousins or closer. Loeske Kruuk, Edinburgh University, Scotland found that

collared flycatchers born from brother-sister matings were more than 90%

less likely to survive to maturity than offspring of non-incestuous matings.

Ilkka Hanski of Helsinki University, Finland found that 50% of male

offspring of brother-sister matings in a certain species of African

butterfly were sterile.

 

Natural isolation and inbreeding have given rise to domestic cat breeds such

as the Manx which developed on an island so that the gene for taillessness

became widespread despite the problems associated with it. Apart from the

odd cat jumping ship on the Isle of Man, there was little outcrossing and

the effect of inbreeding is reflected in smaller-than-average litter sizes

(geneticists believe that more Manx kittens than previously thought are

reabsorbed due to genetic abnormality), stillbirths and spinal abnormalities

which diligent breeders have worked so hard to eliminate.

 

As mentioned, some feral colonies become highly inbred due to being isolated

from other cats (e.g. on a remote farm) or because other potential mates in

the area have been neutered, removing them from the gene pool. Most cat

workers dealing with ferals have encountered some of the effects of

inbreeding. Within such colonies there may be a higher than average

occurrence of certain traits. Some are not serious e.g. a predominance of

calico pattern cats. Other inherited traits which can be found in greater

than average numbers in inbred colonies include polydactyly (the most

extreme case reported so far being an American cat with 9 toes on each

foot), dwarfism (although dwarf female cats can have problems when try to

deliver kittens due to the kittens' head size), other structural deformities

or a predisposition to certain inheritable conditions.

 

The ultimate result of continued inbreeding is terminal lack of vigour and

probable extinction as the gene pool contracts, fertility decreases,

abnormalities increase and mortality rates rise. On the other hand, too much

outcrossing will cause loss of type and therefore the loss of a distinct

breed.

*

 

SELECTIVE BREEDING*

 

Artificial isolation (selective breeding) produces a similar effect. When

creating a new breed from an attractive mutation, the gene pool is initially

necessarily small with frequent matings between related cats. Some breeds

which resulted from spontaneous mutation have been fraught with problems

such as spasticity (cerebellar hypoplasia) in Devon Rexes, skeletal problems

in Scottish Folds and the effects of a semi-lethal gene (aka deferred lethal

gene) in Manxes and the lethal gene in Ojos Azules. Problems such as hip

dysplasia and patella luxation are more common in certain breeds and

breeding lines than in others, suggesting that past inbreeding has

distributed the faulty genes. Selecting suitable outcrosses can reintroduce

healthy genes, which might otherwise be lost, without adversely affecting

type.

 

Just as Fan Tee Cee changed the shape of the Siamese, a cat called Good

Fortune Fortunatus in the 1970s changed the shape of Burmese cats in the

United States and gave rise to the " Contemporary " look now fashionable in

that country. American Burmese changed from being moderate, foreign-type

cats into short-nosed, round-headed, barrel-chested cats which some have

described as " pug-like " . Unfortunately, the " Burmese head fault " , a lethal

condition that requires euthanasia, came hand-in-hand with the

" Contemporary " look. As more people wanted the new look in their breeding

lines, so the lethal defect spread. Burmese cats in Europe, Australia and

New Zealand were not influenced by the Fortunatus lookand are free of the

hereditary fault; in addition, occasional outcrossing to introduce new

colours has ensured that European lines do not become so inbred.

 

Another example of a lethal gene which determines a breed trait is the

blue-eyed Ojos Azules. The gene is lethal in the homozygous form causing

stillbirth, cranial deformities, white fur and a small curled tail. In the

heterozygous form, the Ojos Azules are blue eyed non-white cats. Breeders

must therefore breed blue-eyed cats (heterozygous) to non-blue-eyed cats

(lacking the gene for the eye colour, but having the conformation) in order

to get a roughly 50/50 split of blue-eyed and non-blue-eyed kittens while

avoiding deformed dead kittens.

 

The more that inbreeding is used to get rid of undesirable traits or to fix

a desirable trait, the more likely it is that individuals will also inherit

the same set of genes for the immune system from both parents, and be born

with less vigourous immune systems. The immune system problem is compounded

over successive generations as the animals become genetically more uniform

(like the cheetah). According to one theory, immunodeficiency may be caused

by a simple lack of heterozygosity in the genes that control the immune

system. This is why random-bred cats are generally so robust.

 

Breeder and author Phyllis Lauder wrote in 1981: " Favoured varieties of

today have been bred sire to daughter and cousin to cousin until their

breeds are ruined [...] man's insistence on upon breeding in order to

perpetuate features approved in the show ring has produced animals of weak

constitution, prone to such conditions as skin troubles, lacking in

intelligence, no longer mentally alert, eventually stupid; and at last

breeding with difficulty: a state of affairs leading in the end to the

sterility and death of the breed. "

 

Zoos engaged in captive breeding programs are aware of this need to outcross

their own stock to animals from other collections. Captive populations are

at risk from inbreeding since relatively few mates are available to the

animals, hence zoos must borrow animals from each other in order to maintain

the genetic diversity of offspring. In sheep, centuries of selective

breeding to improve the quality of wool has caused an important trait to be

lost. Ancestral sheep could breed more than once per year. Modern sheep

breed once per year. Only recently has the importance of the lost gene been

realised (i.e. to increase meat yield), but to reintroduce it from primitive

sheep would reduce other qualities selectively bred for over centuries.

 

Most laboratory mice are becoming so highly inbred that they would probably

not survive outside of a sterile laboratory due to poor immune systems (they

are generally killed before this becomes a problem in the laboratory

situation) and some strains become extinct due to reproductive failure. Many

are selectively bred to exhibit defects which will kill them.

 

Inbreeding holds problems for anyone involved in animal husbandry - from

canary fanciers to farmers. Early Turkish Vans were reported to be

temperamental, a problem apparently rectified by the importation of new

stock. Attempts to change the appearance of Burmese cats in America to

produce a cat with a rounder head resulted in cats with congenital problems.

Siamese cats have become progressively finer-boned as breeders strive to

emphasise the foreign look, resulting in frailer cats in some breeding

lines.

 

In the dog world, a number of breeds now exhibit hereditary faults due to

the over-use of a particularly " typey " stud which was later found to carry a

gene detrimental to health. By the time the problems came to light they had

already become widespread as the stud had been extensively used to " improve "

the breed. In the past some breeds were crossed with dogs from different

breeds in order to improve type, but nowadays the emphasis is on preserving

breed purity and avoiding mongrels.

 

Those involved with minority breeds (rare breeds) of livestock face a

dilemma as they try to balance purity against the risk of genetic

conformity. Enthusiasts preserve minority breeds because their genes may

prove useful to farmers in the future, but at the same time the low numbers

of the breed involved means that it runs the risk of becoming unhealthily

inbred. When trying to bring a breed back from the point of extinction, the

introduction of " new blood " through crossing with an unrelated breed is

usually a last resort because it can change the very character of the breed

being preserved (as noted by cat fanciers when Russian Blues were crossed to

Blue Point Siamese after World War II). In livestock, successive generations

of progeny must be bred back to a purebred ancestor for 6 - 8 generations

before the offspring can be considered purebred themselves.

 

In the cat fancy, breed purity is equally desirable, but can be taken to

ridiculous lengths. Some fancies will not recognise " hybrid " breeds such as

the Tonkinese because it produces variants (yet Manxes are recognised and

also produce variants). Breeds which cannot produce some degree of

variability among their offspring risk finding themselves in the same

predicament as Cheetahs and Giant Pandas. Such fancies have lost sight of

the fact that they are registering " pedigree " cats, not " pure-bred " cats,

especially since they may recognise breeds which require occasional

outcrossing to maintain type!

 

The breed purity debate goes along these lines: should a breed be based on

genotype (what genes it inherited) or phenotype (appearance, despite an

out-cross four generations ago) A Tabby-point Siamese is phenotypically

Siamese, but because the tabby pattern was introduced from non-Siamese cats,

genotype-followers consider it " not Siamese " and are worried it will pollute

their purebred breeding lines. In some registries, Exotic Longhairs are

identical to Persians, but may not be bred with Persians. Likewise, some

registries do not allow chocolate or lilac Persians to be classed as

Persians because the colours were introduced from Siamese cats (via the

Himalayan breed) umpteen generations ago and are therefore " tainted " . Those

" tainted " genes may be bundled with whole lot of healthy genes; by not

outcrossing " purebreds " to " tainted " cats, the opportunity to increase the

heterozygosity of the immune system is lost (there is a footnote on

phenotype/genotype/purebred/pedigree philosophies).

 

One formula to reduce inbreeding and slow down the loss of vigour is to

line-breed for 2-3 generation and then out-cross to an unrelated line (or

occasionally another breed) to get back hybrid vigour and genetic diversity.

However with the emphasis on breeding for type and competitiveness on the

showbench (and when making a sale), the typey studs get used more and more

often and there is less and less chance of finding a truly unrelated line.

 

See The Pros and Cons of Cloning

<http://www.messybeast.com/clonecat.htm>for further discussion on

inbreeding hazards should cloning of typey animals

become permissible.

*

 

IMPLICATIONS OF INBREEDING FOR THE CAT BREEDER

*

 

Most cat breeders are well aware of potential pitfalls associated with

inbreeding although it is tempting for a novice to continue to use one or

two closely related lines in order to preserve or improve type. Breeding to

an unrelated line of the same breed (where possible) or outcrossing to

another breed (where permissible) can ensure vigour. Despite the risk of

importing a few undesirable traits which may take a while to breed out,

outcrossing can prevent a breed from stagnating by introducing fresh genes

into the gene pool. It is important to outcross to a variety of different

cats, considered to be genetically " sound " (do any of their previous

offspring exhibit undesirable traits?) and preferably not closely related to

each other. Outcrossing is made difficult by the amount of inbreeding in

previous generations - it becomes hard to find cats which are not related,

sometimes several times over.

 

How can you tell if a breed or line is becoming too closely inbred? One sign

is that of reduced fertility in either males or females. Male Cheetahs are

known to have a low fertility rate. Failure to conceive, small litter sizes

and high kitten mortality on a regular basis indicates that the cats may be

becoming too closely related. The loss of a large proportion of cats to one

disease (e.g. enteritis) indicates that the cats are losing/have lost immune

system diversity. If 50% of individuals in a breeding program die of a

simple infection, there is cause for concern.

 

Highly inbred cats also display abnormalities on a regular basis as " bad "

genes become more widespread. These abnormalities can be simple undesirable

characteristics such as misaligned jaws (poor bite) or more serious

deformities. Sometimes a fault can be traced to a single stud or queen which

should be removed from the breeding program even if it does exhibit

exceptional type. If its previous progeny are already breeding it's tempting

to think " Pandora's Box is already open and the damage done so I'll turn a

blind eye " . Ignoring the fault and continuing to breed from the cat will

cause the faulty genes to become even more widespread in the breed, causing

problems later on if its descendants are bred together.

 

One breed which was almost lost because of inbreeding is the American

Bobtail. Inexperienced breeders tried to produce a colourpoint bobtailed cat

with white boots and white blaze and which bred true for type and colour,

but only succeeded in producing unhealthy inbred cats with poor

temperaments. A later breeder had to outcross the small fine-boned cats she

took on, at the same time abandoning the rules governing colour and pattern,

in order to reproduce the large, robust cats required by the standard and

get the breed on a sound genetic footing.

 

*

 

PROS*

*

 

CONS*

*

 

INBREEDING

*(Mating of closely related individuals)

 

Produces uniform or predictable offspring.

Hidden (recessive) genes show up and can be eliminated.

Individuals will " breed true " and are " pure. "

Doubles up good genes.

Eliminates unwanted traits.

 

Doubles up on faults and weaknesses.

Progressive loss of vigor and immune response.

Increased reproductive failures, fewer offspring.

Emphasis on appearance means accidental loss of " good " genes for other

attributes.

Genetically impoverished individuals.

*

 

LINE-BREEDING

*(Mating of less closely related individuals)

 

Avoid inbreeding of very closely-related cats, but cats are still " pure " .

Produces uniform or predictable offspring.

Slows genetic impoverishment.

 

Require excellent individuals.

Does not halt genetic impoverishment, only slows it down.

*

 

OUTCROSSING *(Mating of unrelated individuals within the same breed)

 

Brings in new qualities or reintroduces lost qualities.

Increases vigor.

Cats are still " pure " .

 

Less consistency and predictability of offspring.

May have to breed out unwanted genes accidentally introduced at same time.

May be hard to find individuals which are true outcrosses.

*

 

HYBRIDIZATION *(Mating of unrelated individuals of different breeds)

 

Brings in new qualities or reintroduces lost qualities.

Increases vigor, may improve immune system and reproductive capacity.

Introduces totally new traits e.g. color. Fur type.

May result in new breeds.

The offspring are considered " impure " for many generations.

 

Unpredictable - new traits may not all be desirable.

Must choose outcross breed whose qualities complement or match own breed.

May take years to eliminate unwanted traits/loss of type.

May take years to get consistent offspring.

Produces many variants not suitable for use in breeding program.

 

 

*

 

GENOMICS*

 

As well as recording matings and tracing pedigrees, modern biologists can

look for genetic evidence of inbreeding in an individual's genome

(genomics). Zoologist Bill Amos at Cambridge University, England analyses

genetic markers to assess how closely related an individual's parents are.

This allows them to look at the effect of inbreeding in wild populaitons,

something previously difficult or impossible as it was not possible to trace

pedigrees. Although not foolproof, blood testing and genetic analysis can

indicate how closely animals are related.

 

As well as inheriting copies of genes from each parent, animals inherit

sections of non-coding ( " junk " ) DNA which can be used as genetic markers and

are known as microsatellites. As well as being homozygous or heterozygous

for genes, animals can be homozygous or heterozygous for these

microsatellites. Even without inbreeding, some markers are naturally more

widespread in a population than others. Looking at several markers at a time

gives a better measure of relatedness (the more markers which can be

tracked, the better the results). Some of those markers may be next door to

beneficial or harmful genes (or, because many genes work in association with

other genes, next door to genes which are influenced by other " good " or

" bad " genes elsewhere in the genome) - in the absence of artificial

selection by breeders, markers next to " good " genes will be more widespread

than those next to " bad " genes because the " bad " genes make the animal less

likely to survive.

 

The technique is not foolproof, but if Amos's currently controversial

calculations do turn out to be correct, inbreeding is more damaging than

previously realised and even cousin-cousin matings may result in inbreeding

depression. His studies suggest inbreeding is more important than

environmental challenges in determining an individual's chances of survival.

The " degree of microsatellite homozygosity " (what Amos calls " internal

relatedness " ) means the number of identical markers. Animals with high

microsatellite homozygosity fare worse than highly heterozygous individuals.

In island-living wild Soay sheep, those with higher homozygosity also had

more parasitic worms and were more likely to be sick.

 

Amos suggests that the disadvantages of inbreeding are more pervasive than

previous suspected. In the past, inbreeding was considered relatively

unimportant compared to environmental challenges such as finding food,

finding mates or avoiding predators. Amos suggests that animals with higher

internal relatedness produce fewer young and suffer more from disease,

parasites or cancer. In nature, inbred individuals tend not to survive; this

removes harmful mutations from the population. Inbreeding depression is

known to affect the immune system. Artificial selection by breeders means

genetically weak individuals, which would normally be weeded out by natural

selection, get a chance to pass on their mutations to another generation

and, being more prone to disease, will need more medical care during their

lifetimes than less inbred individuals.

 

As well as selecting animals for physical traits, it is important to select

them for health traits as the prevalence of Polycystic Kidney Disease in

Persians and Exotics demonstrates. Registries may have to permit more

outcrossing between breeds to ensure the vigour of any single breed.

Currently, many gene pools are closed (no more outcrossing) when the desired

traits are fixed and a certain population level is reached.

*

 

CONCLUSION*

 

Inbreeding is a two-edged sword. On the one hand a certain amount of

inbreeding can fix and improve type to produce excellent quality animals. On

the other hand, excessive inbreeding can limit the gene pool so that the

breed loses vigour. Breeds in the early stages of development are most

vulnerable as numbers are small and the cats may be closely related to one

another. It is up to the responsible breeder to balance inbreeding against

crossings with unrelated cats in order to maintain the overall health of the

line or breed concerned.

*

 

FOOTNOTE: THE CHEETAH*

 

In January 2003, India announced plans to clone cheetahs to help restore the

Indian sub-continent's now extinct cheetah population. India plan to clone

cheetahs from Iran where about 50 Asiatic Cheetahs remain.

 

Cloning creates genetically identical individuals. However, cheetahs are

already so highly inbred that individuals are already almost genetically

identical so the impact of clones on the population will be to increase

numbers rather than further decease genetic variation. If it uses the

leopard's own egg cells it would introduce the leopard's mitochondrial DNA

(the DNA found in an egg cell) into the cheetah population.

*

 

FOOTNOTE: PUREBRED VS PEDIGREE; PHENOTYPE VS GENOTYPE*

 

There is a long-running and often bitter in several cat registries about

recognising and perpetuating breeds based on phenotype or on genotype.

Phenotype means " what it looks like " while genotype means " its genetic

make-up " . The latter requires a cat's pedigree to be known over several

generations and for the pedigree to contain only cats of the same breed.

 

The debate has been a long-running one among breeders of Persian and Siamese

cats; this is hardly surprising as recognition of these two breeds dates

back to the dawn of the cat fancy in the 1870s and 1880s. Should the " new "

colours of Siamese (red points, tortie points etc) be recognised as Siamese

or should they be kept separate e.g. as Javanese, because their bloodlines

are not pure; the same applies to self chocolate and self lilac in Persians

since these colours came from the Siamese via the colourpoint Persian

(Himalayan). Among rare breed livestock breeders, the 7th generation

offspring of an outcross is considered purebred if each generation of

offpring have been backcrossed to a pure bred animal following the initial

outcross. In cat breeding, the only remaining trait from the outcross might

be the new colour, but among extremely pro-genotype cat breeders, that

bloodline is considered forever tainted by the outcross and will never

produce " purebred " cats. Some pro-genotype breeders admit to wanting cat

fancying to remain an elite hobby, with only " purebred " cats tracing back to

original stock being accepted for breeding.

 

Among pro-phenotype breeders, the situation is somewhat different. If it

looks like a Siamese in all respects, apart from the new colour, then it is

accepted as a Siamese regardless of mixed ancestry several generations back.

They accuse the pro-genotype breeders of unnecessary snobbery and point out

the dangers of inbreeding. The separation of the new colours of Siamese and

Persians is considered artificial since the cats' conformation is unchanged.

 

As mentioned earlier, pro-genotype cat fanciers lose sight of the fact that

they are registering *pedigree *cats - pedigree does not mean the same as

purebred! *All *breeds began based on phenotype i.e. what they looked like.

For example, naturally occurring cats with a particular " look " might

gathered together and called a breed e.g. the British Shorthair or Maine

Coon. These are considered natural breeds. Even where the foundation cats

are pedigree members of different breeds, the new breed is selected for, and

refined, according to its appearance. In the early days of a breed it

sometimes becomes necessary to accept cats of unknown ancestry but

appropriate appearance into the breed to expand the bloodlines and prevent a

dangerous level of inbreeding. All breeds have to start somewhere - and that

somewhere has a phenotypic basis.

 

One danger, pointed out by pro-genotype breeders is that accepting

" lookalike " cats into a breed with a known genotype can introduce unwelcome

unknown genes which could become widespread and result in undesirable traits

later on. If the two faction, pro-genotype and pro-phenotype, diverge any

further, it will result in different variants of breeds being recognised -

not just a split along tradition vs classic vs contemporary lines, but a

split along the lines of " Phenotypic Siamese " and " Genotypic Siamese " with

the two strains no longer being interbred for fear of taining the

genotypically " pure " variety. Isolating a strain to keep its genotype pure

means it will inevitably become inbred.

 

There needs to be a sensible balance. When enough generations have elapsed,

a descendant far removed from the original outcross is, to all intents and

purposes, purebred. The variation in its genes from the outcross is probably

no greater than the variation due to natural mutation. Breeds in their

infancy may need to pursue phenotypic breeding programs until the gene pool

is wide enough to support breeding along genotypic lines. To revisit the

example of Siamese cats - the early imports may have been seal and the

earliest colours seal, blue, chocolate and lilac, but in their homeland, as

I have witnessed on the streets of Malaysia and Thailand, colourpoint cats

occur in all colours! It is only a quirk of cat fancy history that has led

to those first four colours being declared true Siamese colours and the

others being considered " introduced " colours.