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Chihuahua Genetics

Basic Genetics
Coat Genetics
Size Genetics
Genetic Faults

Basic Genetics

Article: Basic Genetics
Author: MindiBown Kennels

Almost everyone, whether they're involved in breeding of any kind or not, is familiar with the terms Dominant & Recessive.
The easy trap to fall into here is to believe that ALL genetics is of a dominant / recessive nature. Sorry to disillusion you but that is not the case. However, this simple type of genetic structure is a good place to start in our studies. To illustrate our point, let's take a classic example which is also pertinent to our breed.

The Genetics of Long vs Smooth Coat Chihuahuas

All genetic studies should start with the simple explanation that each gene, regardless of what it controls is basically made up of two parts. These parts are referred to as alleles. We inherit one allele from our mother and one from our father. The two alleles, when combined form a single gene. That gene may be the one that controls the colour of our eyes, or perhaps the colour of our hair. In the case we are looking at here, they control whether the dog will have a smooth or a long coat.

To begin, let's first of all understand that at this level of genetic study we will assume that there are only two possible alternatives to a particular trait. In this case, long or smooth.

Next, Let's accept that there are only 2 alleles in each gene.

Now that I've said that, I must point out that this is NOT the case in every instance. Size for instance is made up of 6 alleles. 3 from each parent.

Colours may have 4 or 5 or even more possibilities, (or alleles) to choose from.

But for now let's be happy with the simple version.

Ok, there are two possibilities. Long or smooth. In the case of Chihuahuas, smooth is dominant.

What does this mean?

Quite simply, if a pup inherits a smooth coat allele from either parent, it WILL be a smooth. Even if one parent is a long.

Look at it this way:

Dog 1Dog 2Dog 3
As only Long alleles are present, this will be a Long Coat dog As only Smooth
alleles are present, this will be a
Smooth Coat dog
Both Long and Smooth are present, but the Smooth is dominant. Therefore this dog will be a smooth.


Now what would happen if we bred Dog 1 with Dog 2?

Remember, each parent contributes one allele to their offspring. Logically they can only give what they've got.

2 possibilities from 2 parents means there are 22 = 4 combinations possible.

Ok, that was pretty predictable. We have four identical pups. Each one is a Smooth, but each one carries a Long Coat Allele. By the way, please forgive us breeders when we say that a dog "Carries a long coat gene" Technically that is incorrect. They carry a long coat ALLELE. But hey, if we were smart, we wouldn't be dog breeders.

The thing to remember here is that if you are looking at a bitch or stud dog. If that dog is a smooth, but has a long coat parent, he or she is like the pups above. They can throw a long coat pup. (Given the right partner)

Now, let's try a more interesting combination with less predictable results. How about 2 like dog 3?

What have we got?
Pup 1 is a long. That's obvious.
Pups 2 & 3 are smoothes, but carry a long coat allele.
Pup 4 is a smooth.

So out of 4 pups, 3 are smoothes.

According to the laws of genetics, this is so. HOWEVER!

We also have to deal with the laws of probability or chance.

Toss a coin into the air and what are the chances of it coming up heads? Right....50/50
Toss that same coin into the air 10 times. Will it come up heads 5 times?
Maybe, maybe not.
So far this is primary school stuff. Now, if you toss that same coin in the air 10 times and it comes up heads every time, what are the odds of it coming up heads on the 11th toss?
Answer? 50/50 !....Don't agree? That's what makes two-up such a deadly way to lose money!

Dogs are the same. You combine the genetics of two dogs that SHOULD give you what you are looking for, and then sit back and wait to see if the coin comes up heads, and you get what you want, or tails, and someone gets themselves a new pet Chihuahua.

Now here's one for you to figure out.

If we put two like dog 1 (Long/Long) together, what would we get?

I'm not going to slow the loading of this page down any more by putting in another diagram. This one is easy. Each parent can only pass on what they've got. A long coat dog has only long coat alleles to give therefore every single pup will be a long. PERIOD!

Do you know there are breeders who will insist that they've had a smooth from a double long breeding?

Genetically speaking, it is impossible. Now, before assuming that a breeder who makes this claim is therefore dishonest, let me say there are 3 possibilities.
1. The (most obvious) A smooth coat dog got somewhere he shouldn't have. This is probably the explanation in 9 out of 10 cases. However there are 2 more possibilities

2. The pup is actually a long coat, but with such a terrible coat that it resembles a smooth

or

3. The pup is the result of a mutation.

This third option is a distinct possibility, although the odds against it are enormous.

A similar situation exists in the Saluki breed. There are 8 documented and DNA confirmed cases in the USA in the past 20 years.

By understanding the genetics involved, you may begin to understand one of the reasons a smooth/smooth is so valuable to us. What this means to a breeder is that every single pup a smooth/smooth produces WILL be a smooth. There is just no other possibility. This predictability is of great value to us. One effective way of improving a long coat is to bury the long coat gene (allele) for a generation. A smooth/smooth will do that. Put a male smooth/smooth to a long coat female and you can only end up with Long/Smooth pups. The pup itself will of course be a smooth. But in the next generation if we put that Long/Smooth pup to a Long/Long partner, we will have the long coat back, hopefully better than before. That's the theory anyway. In practice of course, it's a toss of the coin.

I guess in the long run, breeding has and always will be just like tossing a coin. A sound knowledge of genetics however, can at least insure that you aren't using a double headed coin.

(C)Copyright 2007, this article is copyright protected
Special thanks to MindiBown Kennels for permission to display this article on RoyaltyChi Chihuahuas website

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Coat Genetics

Article: Colour Genetics
Author: MindiBown Kennels

Probably more than any other area of breeding, the study of colour inheritance is the most fascinating, and probably the most misunderstood. A relevant observation is that it is also harmless. ANY colour is acceptable in our breed. Therefore if we try to figure the genetics of colour and miss, it really doesn't matter. So adopting the principle adage of the medical profession, "First of all, do no harm" this is a good place to experiment. You won't end up with a deformed or crippled pup. I'm certainly not suggesting that anyone should ever put two dogs together purely and simply to chase a certain colour, but trying to predict Colours before the whelping is an interesting diversion.

The genetics of colour is also a logical next step in this series of articles as the predominate nature of these genes are still of the old popular recessive/dominant variety.

In this area however, we learn of two extra components of Genetics.

The first is an extension of the study of coat inheritance factors. Genes in this area still have only two parts to them, one from Mum and one from Dad, but we are now faced with a lot more choices of possibilities that can be passed on.

The second is the discovery that one gene can have an effect on another gene further down the DNA trail. In fact, in colour, several different genes can act upon each other to produce a colour. In some cases, one gene will mask, or counteract the presence of another.

Oh, before we start. From here on I'm going to use the accepted terminology in genetics to signify recessive or dominant. Namely, a capitol for dominant. "B" or lower case for recessive "b".

Let's start with the pattern or presence of white.

There are 4 parts to this allele.

In order of dominance:

            S : "Self coloured", No white showing. (Most Dominant)
            si : "Irish Marked". i.e. white feet, tail and collar
            sp: "Parti colour" (two or more solid colors, one of which must be white)
            sw : Almost all white, very little, if any colour.


Now these are all listed in order of dominance. A solid colour dog is probably carrying the "S" allele. Because this is the most dominant. However, the other half of the gene may be any of the others.

On the other hand, if you had two parti colour dogs and bred them, they could only produce more parti's or an almost pure white. If you had your heart set on an Irish marked pup, forget it. It's genetically impossible. Of a more practical nature. If you are offered an Irish marked pup supposedly from two parti colour parents, walk away. That breeders pedigrees aren't worth the paper they're written on.

Next, let's look at the pattern of black.

Again, in order of dominance.

            A: Results in pure black. The strange thing is that despite this being the most dominant, an all black Chihuahua is seldom seen.
            ay: This is the gene (Allele) that produces the "Sable" effect. Black hairs interspersed through another colour.
            as: Produces a black blanket, usually on a tan body. Very similar to a GSD.
            at: The most recessive, although not at all uncommon. This allele produces the common "Black & Tan" markings as seen on a Doberman, or English Toy Terrier.

A Black & Tan dog can ONLY carry a gene made up of at/at . No other combination is possible. If this statement makes sense to you than you are getting a good grasp of the basic concepts of Recessive/Dominant Genetics.

There are a number of interesting points about this set of alleles. (By the way, a set of alleles such as this is referred to as a "lotus") The first is that despite the A allele being the most dominant, an all black Chihuahua is seldom seen. Why? My personal theory is that it's because black dogs are not popular in the show ring. Their colour tends to disguise their good points and accentuate the bad. For this reason a lot of breeders won't breed an all black dog. The danger here is that it would be easy for the option of a solid black dog to completely and IRREVERSIBLY disappear. The easiest inherited trait to breed out is one caused by a dominant allele. It is my personal belief that this is an example of breeders choosing to breed for success in the show ring, rather than a genuine desire to improve the breed. E.O.S. (End Of Sermon)

There is one more lotus of alleles that affect the black on a Chihuahua.

            Em No matter what other genes are active, this allele will put a black mask on it.
            E Next most dominant, this results in no black mask.
            ebr Brindle. To those unfamiliar with the term, sort of irregular vertical black stripes. Not particularly rare in Chihuahuas but not overly common either.
            e The most recessive of this lotus, this allele MASKS black anywhere on the dog.

Now think about this last allele for just a minute. This is a wonderful example of genetics disguising things, and of the ability of one gene to affect another totally separate one. Let's say you have a dog that is at/at . Black and Tan. (In accepted genetic terminology we say the the dog is of the at/at genotype) Now if the e allele is also present you will have an all tan dog. One might say a Black & Tan for people who don't like Black & Tans.

So far we have covered the gene that controls white (S) and black (A) & (E)

Now let's have a look at the genes that control colour and it's shading.

There are basically 3.

The first

            B Allows black to be black. (Sort of the opposite of e)
            b Makes all black hairs appear brown. (Chocolate)

Let's stop here and have a closer look at this b gene. The Chocolate Gene. It's another example of one gene altering another one someplace else.

In this particular case we can see that two totally separate and distinct genes must be present for the chocolate colour to appear. The first one is any member of the A lotus. There has to be some black present. The second is the b allele, which will turn that black to chocolate.

There's an interesting marker or flag for the b allele. It gives the dog a brown nose and yellow eyes. This then makes the breeding of chocolates rather easier to predict. If you have a cream or tan dog (or any other colour) with yellow eyes and a brown nose, it carries the chocolate gene. All you need now is some black in it's breeding partner and hey presto, a percentage of the litter will be chocolate.

If only all recessive genes carried a flag like the chocolate gene does. Life would be so much easier.

It's also interesting to note that I recently saw an ad on an American Chihuahua breeders Web Site offering a pup for sale as a pet. The reason given was that it had a self coloured or brown nose, and she was trying to breed this feature out of her kennels.

I had to ask myself whether she was saying that chocolate was an unacceptable colour to her, or did she not realise that the brown nose was merely part and parcel of the chocolate gene?

I tend to think that it was the latter. That is rather unfortunate as it means that a quite experienced breeder in fact has no knowledge of even basic genetics in her breed. Sadly, this is the case more often than you may think.

Next we come to:
            D Makes all Colours intense and full. e.g. Black is Black
            d The opposite. Makes all Colours less intense, or diluted. This gene in an otherwise black dog will wash the black out to a grey colour. Our so-called "Blue"

And lastly:
            C Similar in effect as D. Allows Colours to be fully saturated.
            cch Decreases the saturation of colour while allowing black to remain black. Most rare in Chihuahuas, this gives us a Chinchilla effect. Hairs that are black at the tips but light at the roots. Most often the root colour is either a blonde or smoky grey or white. VERY pretty, and very rare.

So there you have it. Do you think you now know all about predicting Colours in a Chihuahua? Fantastic! E-mail me will you and explain it to me!

The more I study genetics, the more questions I seem to come up with.

For example. Is there an order of dominance between the lotus'? There must be. Has anyone EVER seen a parti colour with a black mask? That would suggest that if the Sp allele is present, it is dominant over the Em allele.

Can anyone explain cream? I know from observation that it is very dominant. (There hasn't been a single ChaChi litter that isn't 50% creams) But it's not mentioned anywhere in the text books. Is it in fact Tan diluted by the d allele. If this was so, we'd expect more blues from cream dogs and that doesn't seem to be the case.

I'll close this subject with a final observation. I made an earlier comment on the number of breeders whose knowledge of genetics is sadly lacking. If you are a student of our breed however, do NOT dismiss what an experienced breeder says even if they come out with a statement that proves their technical knowledge is minimal. (I have a long coat girl that ALWAYS throws longs no matter who you put her with) What you'll find is that a lot of breeders have noticed trends over the years that although they may not be able to explain genetically, they are none the less valid.

A good example is blues. We now know that a Blue Chihuahua is a combination of the A, (Black) and the d (dilution) allele. I have not been able to find a single reference in any book, article or journal that would even remotely suggest that the dilution or d allele is in any way connected to the chocolate or b allele. However, breeder after breeder has stated quite categorically that "blues come from chocolates".

What do you make of this contradiction? In my case, I take the view that what these breeders have seen is valid and probably correct. We just can't explain it yet.

Listen to what they have to say and then study some more and see if you can then logically explain what they have seen. Or, perhaps break new ground and prove them correct scientifically.

(C)Copyright 2007, this article is copyright protected
Special thanks to MindiBown Kennels for permission to display this article on RoyaltyChi Chihuahuas website

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Size Genetics

Article: The Genetics of Size
Author: MindiBown Kennels

I'm sure at least some of you have wondered at the amazing variation in size when looking at Chihuahuas.
Of even greater mystery may be watching 2 normal or even quite large parents produce a tiny, tiny offspring.
How can that happen?

It's pure genetics.

The gene that controls size is different from most in so much as it has 6 parts, or alleles, and that each parent passes on 3 of theirs. Which 3 is pure Tattslotto stuff. Spin the wheel and see what numbers drop.

The size alleles can be best described as either + or -. We then add the 6 together and get a total. With six present in any living mammal we have an infinite variety of variations.

For example: +,+,+,-,-,-, = 3 of each. Think of the +'s as "up 1", and the -'s as "down 1" The first three cancels out the next three so we end up with 0, or your proverbial "Average".

How about +,-,+,-,-,-. Add them up and we get 2 up and four down. end result = 2 down or below average size.

One more. +,+,+,+,+,-. 5 up and 1 down = 4 up. or in other words, a BIG boy.

Are you starting to get the idea?

Ok, let's start passing things on to the kids.
Let's take 2 average parents. +,+,+,-,-,-. = Dad and +,+,+,-,-,-. = Mum. Let's give them a litter of 3.

Pup 1. We'll take (at random) -,-,+. 2 minuses and 1 plus from Dad and let's say -,+,+. 1 minus and 2 pluses from Mum.

Pup one therefore is -,-,+,-,+,+. up and down we end up back at 0, or average size.
An average size pup from 2 average sized parents. What else would you expect?


Well how about Pup 2?

We'll have -,-,-. 3 minuses from Mum AND -,-,-. three minuses from Dad. What size pup do we get?
-,-,-,-,-,-. down, down, and down again 6 times means one very tiny pup.

For Pup3

We'll go the opposite. Let's have all the pluses that both Mum and Dad can give.
That's a total of +,+,+,+,+,+. 6 ups or a Chihuahua masquerading as an elephant.

AND ALL THREE FROM AVERAGE PARENTS
That's the best part.

But when you see how size is inherited, it all starts to make sense doesn't it?

But genetics is only half the story with size.
It's been fairly well documented that the human race is getting bigger and bigger with each generation. When you look through museum reproductions of early settler's cottages etc. the height of doorways and the length of beds stand out as being so small by today's standards.

This growth in the human population has been put down to an improvement in diet and better health care.

Science has pretty well proven that diet has played a major role in this phenomena. Diet is just one factor in what is generally referred to as "Environment". And environment plays a major role in the size of Chihuahuas as well.

There is more to size in Chihuahuas than pure inherited genetics. Environment plays a definite role, as does an as yet unknown genetic link to problem areas in the Chihuahua physique that inhibits growth.

Some years ago when we had not long been breeding Chihuahuas, we had occasion to have a litter arrive in the depth of winter. As luck would have it, that particular time coincided with a breakdown in the family chain saw. Hence, our supply of firewood was being rationed. In short, the house was b.......y cold.

The litter arrived and they were all fit, healthy and eating well. It wasn't long however before it became obvious that all was not well. All pups cry, but this litter cried non-stop. In particular, at night when the fire had died down. We realised the pups were cold and we went out and invested in our first heat pad. A good thermostatically controlled unit.

As soon as the pups were put on the heat pad, the incessant crying stopped. The interesting part however was observing the pups weight. It has always been our practice to weigh each pup daily. This litter had shown a small but steady gain each day. A bit down on normal but regular and consistent. As soon as the heat pad was installed the pup's weight gain increased DRAMATICALLY. Not just a little bit but significant and noticeable. On a graph, the weights all took a sudden surge upward.

So what does this mean? Quite simply, that environment also plays a part in puppy growth. Environment is meant in this case to entail both diet and the environs of birth. Quite obviously diet and such has a bearing on growth. The only question is whether the effect is temporary or permanent.

The last factor is a congenital factor affecting growth. Research from the Genome Project has thus far shown a link between size and certain organ development such as the Thyroid. What is not certain as yet is whether size is affecting the development process or the development of certain organs and glands is affecting size.

It seems pretty obvious however that the very tiny tiny examples of our breed have more health problems than their normal brothers and sisters. At this stage it's still a "Chicken & Egg" discussion, but the connection is obviously there.

The one over riding conclusion that should be emphasised is that the deliberate down sizing of our breed below a (say) 3 lb limit is downright foolish. I would go so far as to suggest a change in the standard to give a preference for a size range of 4 1/2 to 5 1/2 lb.. Not the current, smaller is better with no lower limit.

(C)Copyright 2007, this article is copyright protected
Special thanks to MindiBown Kennels for permission to display this article on RoyaltyChi Chihuahuas website

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Genetic Faults

Article: Genetic Faults
Author: MindiBown Kennels

Selecting for the elimination of genetic faults falls into three broad categories.
99% of faults in the purebred dog are caused by either:
1. Dominant genes
2. Recessive genes
3. Polygenitic genes


Dominant

Faults caused by a dominant gene are a non issue. To the best of my knowledge there are none. Well, none that is common anyway. Quite simply, If a dominant gene caused the fault, it should already have been eliminated.

The reason for this is simple.

In the case of dominant, if a dog carries the gene, it also exhibits the problem. The answer is simplicity itself. Don't breed from that dog. The fault is removed from that line in a single generation.

Recessive

Faults caused by recessive genes are slightly more difficult to remove. The reason for this is because the dog may CARRY the gene that causes the problem but does not actually suffer from the problem itself.

Let's take PRA (Progressive Retinal Atrophy) as an example. This is not a problem found in the Chihuahua but I will use it as an example of a typical recessive problem.

Because a recessive gene causes PRA, a dog that actually suffers from the affliction MUST by the nature of genetics carry two copies of the gene. ALL offspring of that dog therefore WILL inherit one copy of the appropriate gene. If a dog shows clinical signs of PRA, it must be removed from your breeding program.

(I say that with some reservation, as there may well be a circumstance where you WOULD breed this dog. For the purpose of this article however I will take the simple approach. I will cover why breeders will sometimes knowingly breed from a dog with a fault in another article)

Unfortunately the problem doesn't end there.

It is quite possible for a dog to carry a single copy of the PRA gene and it will NOT actually develop PRA itself. No amount of clinical testing will ever show you that PRA exists, because it doesn't. The dog is healthy.

However, put two such dogs together in a breeding and a percentage of the offspring will inherit a copy from both Mum and Dad. These pups will develop PRA as they get older. They now have two copies of the gene.

A percentage of the offspring will inherit one copy from either Mum or Dad. These pups will never develop PRA themselves but WILL carry it to the next generation. For this reason, breeders commonly refer to such dogs as carriers.

Of course, a percentage will also inherit nothing and will neither exhibit the problem nor carry it. They will be healthy dogs and will produce healthy dogs.

The only known way of combating a recessive problem is in an understanding of how it flows from one generation to another, and an accurate pedigree system so that you know both the ancestors and progeny of any given animal.

(I'm ignoring DNA tests as a possibility as they are available in relatively few cases)

There are a few things that you will know for sure that will help in combating this type of problem. Firstly, if a dog in your kennel develops PRA, you know positively that BOTH parents are carriers. I've often heard breeders say that a problem known to be caused by a recessive gene was caused by a certain line of dogs.

“ I've never had that in my kennel until I used xyz stud. Obviously he caused it”

Wrong!

For a problem such as PRA to develop, the pup has to get a copy of the appropriate gene from BOTH parents. Your bitch may have never produced the problem before, but that merely means she's never used the wrong stud before.

This knowledge is really your best weapon.

How?

Because now you can start tracking back and forward in the pedigrees.

Tracking Back

Quite frankly, tracking back in a pedigree is a useless exercise unless you are in one of those rare situations where it is known POSITIVELY which dog brought the problem into the country or area. This does occasionally occur and if you find yourself in this situation, you can draw a line from your dog directly to the known introducer. From this you know that every single dog in this line IS a carrier. Furthermore, you also know that every pup ever produced by any of these dogs COULD also be a carrier.

Tracking Forward

Tracking forward in your pedigree means knowing that every single pup produced by EITHER parent COULD also be a carrier.

From that point on, it's decision time.

If the problem you're dealing with is serious, and you're determined to eliminate it at all costs, you would remove ALL of the suspected carriers from your breeding. If doing this eliminates a big chunk of your breed, that's probably not a smart move.

More commonly, the knowledge is filed away to be used as one more consideration when planning a breeding.

When the time comes to decide which bitch goes to what dog, you have to ask yourself,

“What might I possibly GAIN from this breeding?”

Good tail set, improved ears and a more assertive temperament.

What might I possibly LOSE from this breeding?

Too much height, and a PRA carrier or sufferer.

It's YOUR call. You're the breeder.

Some examples of just some of the problems believed to be caused by a recessive gene:
  • Diabetes mellitus
  • Pancreatic insufficiency
  • Collie eye anomaly
  • Dwarfism
  • Cleft palate (? Geneticists are uncertain)
  • Absence of rear dew claws
  • PNA
  • B12 vitamin malabsorption
  • Copper toxicosis
  • Lipid storage disease
  • Myasthenia gravis
  • Nephropathy
  • Peripheral vestibular disease
  • Scottie cramp

    You'll be pleased to know that none of the above problems (excepting cleft pallet) are common in Chihuahuas

    Polygenitic

    If you intend to be a dog breeder, Polygenitic is a good word to learn. Quite apart from the usefulness of knowing it's meaning, you can have a lot of fun with it.

    Some day you'll be in a group of breeders and one will start to try to impress the others with their knowledge of genetics. They'll throw words like dominant and recessive around like confetti. All you have to do is make a simple comment with the word Polygenitic in it……then sit back and time how long it takes the other breeder to change the subject. The fastest I've seen is 2.5 seconds.

    The word Polygenitic actually describes a trait rather than a gene. The best way to explain this trait is to go back to recessive/dominant again. In simple genetics a feature is either on or off. There or not there. A dog is either black or it isn't etc.
    A dog has PRA or it doesn't. You don't see a mild case of PRA in one dog and a more severe case in another. That's the nature of dominant/ recessive.
    But some things aren't just black and white. There can be a range of grey in between. Anything that can occur in degrees is usually termed a Polygenitic trait, or is said to be of a Polygenitic nature. If anyone asks you for an example, say “Size”

    Think of a problem that comes in degrees of seriousness. There's a good chance it is Polygenitic in nature.

    Within our breed, the example I will use is the scourge of the Toy Dog group, Luxating patellas. Another example I could have used is Hip Dysplasia.

    These are afflictions that can range from very mild to quite severe. A typical Polygenitic trait.

    Now, I'm going to ask you to stay with me. This concept is actually easy to understand once someone has explained it to you. The difficulty is in the explaining. Once you understand, try to explain it to someone else. You'll see what I mean.

    When dealing with problems such as luxating patellas, you must follow a set pattern.

    Step 1. You must have a way of grading the problem from no problem through to severe problem. Within reason, you should have as many gradients as you can handle. The grading system we use in our kennels for patellas has 5 levels, from 0 to 4. Make sure that what constitutes each individual grading is very clear in your mind.

    Step 2. Come up with a maximum grading that YOU believe is the most you will accept.
    That's the hard part!
    Let's look at what you DON'T want to do.
    1. Select a level that is too permissive.
    Let's say you chose “I won't breed with any Chihuahua that is physically unable to walk”
    Big deal! You'll eventually reduce the problem somewhat but can you live that long?
    2. Select a level that is too restrictive.
    Let's say you decide, “I'll only breed Chihuahuas with perfect patellas” With the current level of the problem in our breed, you've just eliminated 90% of all the Chihuahuas in Australia, including a lot of the best ones. What you will end up with if you breed only from the remaining 10% is a bunch of butt ugly Chihuahuas with very strong knee caps.

    Here's what you're aiming to do. Eliminate the worst cases and breed only from the rest.
    What level that is, depends on how bad your dogs are now.

    Let's say you have a really bad problem right now.
    You may chose to only eliminate the grade fours.
    (Actually, if your problem were that severe I would suggest you find a bunch of good pet homes and start again. But let's go on just to illustrate the point.) Having eliminated all the grade fours you would then breed only from grade 3’s or less. But surely you must have at least one dog that is a grade 1 or 2. Think about putting those two dogs together. (Assuming there is no other reason for not doing so, such as they are brother and sister.) Or perhaps you can look outside your kennels for a sound stud dog. What you are coming up with is a total score of all four patellas between 2 dogs. If your worse dog has a grade 3 on each patella, and your best Stud has 2 grade 1’s, your total score is 4+ 4+1+1= 10. As I said earlier, if that really is the best you can do, I'd start again. But if that weren't possible you'd have no choice. Do it! The progeny of this breeding should come out with a slightly reduced problem. Let's say the next generation allows you to put a bitch with a 4 and a 3 with a stud with two 1’s. You've made an improvement haven't you? If you keep this up you will eventually get where we are now. Our maximum permissible score is now 3. You started your program at 4, and you are doing the figures now, to see if you can reduce the maximum score to 2. So your just waiting to have some updated gradings done and you can see where you stand.

    A couple of points on your grading system:
    1. Be totally clear on what constitutes each level.
    2. . Be consistent in that grading. In the case of patellas, it's best to have it done by a vet. Make sure you use the SAME vet each time so there is a consistency in the grading. We've just changed vets so all our dogs are being re-graded by our new one. There was nothing wrong with our old grading except that it was done by someone else. We need to be sure that if a new dog is graded at 0,0 by our new vet, that we can comfortably assume it be the same as a 0,0, from our old vet.
    3. . Remember that the goal is constant and steady improvement, not to fix the problem overnight.
    4. . And lastly. It's no good fixing one problem if in the process you have allowed another one to get a stronger toehold in your kennels. In other words. Don't just attack patellas and ignore all the other aspects that you are aiming for in your breed.

    Not Just Patellas

    This method can be used on any problem that occurs in degrees. We have just turned our attention to the soft palette problem in our breed. From what research we have been able to do we can find no positive source that would indicate that this is an inherited trait and if so, by what degree.

    We are going to have to assume that it is Polygenitic in nature purely due to a lack of feasible alternatives.

    Our first step is to totally understand precisely what is happening inside the throats of our dogs. This we have accomplished.

    The next step is to insure there are no other possible explanations that may cause the same type of breathing difficulty.

    Then, and only then we can try to come up with a grading procedure. This won't be as easy as patellas and initial conversations with our vets have not proved promising. We now have two separate vets thinking about our request and trying to come up with a solution. It may prove difficult to do accurately but in this case I think we have to adopt the policy that a poor grading system is better than no grading system.

    Once that is accomplished, we will do precisely what I've described above with selecting our worst and our best and choosing an acceptable level to start.

    (C)Copyright 2007, this article is copyright protected
    Special thanks to MindiBown Kennels for permission to display this article on RoyaltyChi Chihuahuas website

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