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Old 25-04-2007, 01:26   #59
Dharkwolf
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Ok – this is just a quick overview on the genetics and expression of fur length.

The length of fur in all animals (and of hair in humans, incidentally) is controlled by the hair cycle. (Have to love the original names of these things)

Basically each growing fur strand goes through three phases –

Anagen – This is where the fur is actually growing – ie the strands are lengthening.
Catagen – This is where the fur is in senescence – no longer growing but not shedding either, it’s actually an intermediate phase.
Telogen – This is where the old fur is actually shed.

It probably makes more sense when you actually look at a picture like this one:



Ok – so far so good?

This means in fact that the length of each individual fur strand is determined by two and only two factors:

The rate of growth of the fur
The duration of the Anagen phase (the more time fur spends growing without falling off, the longer the fur will be)

Now for some time there has been this theory going round that a certain gene (FGF5 short for fibroblast growth factor 5 for those of you who like to keep track of these things) that controls the length of the anagen phase. The dominant version of the gene results in a short anagen phase, and therefore in short fur. The recessive version of the gene results in a long anagen phase and therefore long fur.

There is a nice little diagram which explains this one too:


Image from Kingston K.L. Mak et al.

This theory was proven in canines 2006 by D.J.E Housley and P.J Venta which showed that for a number of breeds the short haired version of the dog would have the dominant version of FGF5 and the long haired version of the dog would have the recessive version of FGF5. This was the case in German Shepherds, Corgies, Collies (Border, Smooth haired, Long haired varieties), etc.

Great right? That explains everything!

Well actually it doesn’t. For a number of reasons:

First – the actual hair growth cycle is far more complex than all that. FGF5 works by prolonging the time in Anaphase, but what about factors that affect the actual growth rate of the fur? For instance it is known that there are (undefined) genetic factors in cats which nullify the presumed recessive effect FGF5 – ie if you cross two long haired cats you may get a short haired one (this happens in Persians now and then) This would never happen if you believe in a single determinist factor for fur length – and yet it happens.

So the story is more complicated – here are a few things which are obvious to any wolfdog owner and which really complicate the story in two ways, both by looking at the effect of the coat (as opposed to individual fur strands) and because of the possibility of having other factors come into play:

There are at least two different kinds of fur on a wolfdog – underfur and guard fur. Their length is obviously different so there must be other factor(s) that control the length of the underfur relative to the guard fur.

The winter coat and the summer coats are markedly different – I have not seen any comparative studies on the fur lengths of the coats, but you will probably find that particularly the underfur will have a different length in the winter coat and in the summer coat.

The fur is simply not of equal length all over the body of the dog. Think about it – fur around and within the ears is normally much shorter than that around the rest of the animal. Males are known to have “manes” of longer fur around the collar/neck area (though this effect is also due in part to denser underfur in this area), also the fur on the tail seems to be longer that that on the body (though again – this would need more rigorous study, and is based on casual observation of wolfdogs. I don’t go around pulling out fur from different parts of my girls to check how long they actually are)

It is impossible to explain all of this with the basic “recessive long fur, dominant short fur” model of dog fur. Also it is interesting to note just how short the short fur model is – for instance Dalmatians are said to be normally carriers of the short fur version of FGF5 and I think everyone will agree that if a wolfdog had fur as short as a Dalmatian, there would certainly be something wrong.

So – is there a dominant/recessive gene that affects fur length? Sure, but it only affects the length, it does not determine it. Other factors can be equally important in determining fur length. The genetics of this story are far more complex than simply talking about Mendelean genetics.

One final note on the genetics, there are two ways of determining whether a dog is a carrier or not of a long fur recessive gene – one is breeding with a mate that is known to be a carrier of the recessive gene (not a great idea – but you would expect to get roughly ¼ of the pups longhaired) and the other is to simply test for the variant gene. (for instance this lab offers the test – as well as a few other interesting ones, no affiliation in case you were wondering) Simple no? (Interestingly you can test for quite a few things these days)

As for the wolfdogs themselves and what the implications of this are –

First, don’t judge by photos – it is nearly impossible. If you are going to do so, examine areas that normally would not have long fur. For instance the photo displayed above of Ciro does not in any way show a long coat – if it did the fur around his ears would be abnormally long. It is just the thick winter fur of a male that is made even more prominent because the shot highlights the mane.

Second – looking for the genetic cause for long fur the first thing to look for is FGF5 – there are already commercial tests which will tell you if a dog is a carrier of the “long hair” or the “short hair” version of the FGF5 gene. The solution is there to be used.

Third – and perhaps more tricky – should long fur be selected against, for or neutral? From my point of view the answer is simple – long fur is a fault and should be selected against for a number of reasons:

1) It clearly does not conform with the standard
2) It is likely to impair the working ability of the dog, as the dog is likely to be less resistant to weather conditions (longer fur means that the fur is more likely to get tangled, and paradoxically excessively long guard fur is usually indicative of poor underfur – resulting in worse insulation which can be a problem in warmer, colder and wetter weather conditions)
3) It is very easy to select against. All you need to do is look at a dog (not a photo) to see whether a dog has excessively long fur or not. Of course you can bicker over it, but while it may be difficult to decide whether a given dog has normal or longish fur, excessively long fur is really easy to see (just look at the tufts of fur around the ears, they tend to be easy to spot). If you cannot select against such obvious faults, then the ability to select against more subtle (and possibly more serious faults) is likely to be called in question, it can and will damage your reputation as a breeder. So don’t do it!

Anyhow hope that made it clear. For those of you who are really interested in the genetics of this story I recommend the following references:

Kingston K. L. Mak and Siu Yuen Chan (2003)
Epidermal Growth Factor as a Biologic switch in Hair Growth Cycle
Journal of Biological Chemistry; - Vol 278 No 28 pp 26120-26126.

D. J. E. Housley, P. J. Venta (2006)
The long and the short of it: evidence that FGF5 is a major determinant of canine 'hair'-itability
Animal Genetics 37 (4), 309–315.
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