Blue in dogs is not, in fact, a colour but a colour paling effect which dilutes the colour of the pigment in coat, skin and eyes and is more properly called 'blue dilute'. Colour paling is all it does; it does not affect type, conformation, soundness, or health. A 'blue' dog may be atypical, unsound, unhealthy, or have incorrect conformation but none of those things are caused by his having inherited blue dilute anymore than they would be caused in a 'normal' coloured dog by his being grey brindle, red, fawn, or whatever. A 'blue' dog is as likely [or unlikely] as a 'normal' coloured dog to be typical, sound, healthy and with good conformation, with the proviso that in some breeds there may be variation in type in the different coat colours within the breed.
Blue is an acceptable colour in some breeds, such as Gt. Danes and Greyhounds. In these breeds the colour of the 'blues' is, in fact, the effect of blue dilute on black. Weimaraners are 'blues', although they are not known as such. However, the colour of the Weimaraner is caused by blue dilute on chocolate, and it should be obvious from this that blue dilute is not harmful in any way or this breed could not exist.
Because of the wide range of normal coat colours in the Irish wolfhound - any of which can be inherited together with the blue dilute - 'blues' in our breed are not always readily recognisable. It is certainly not true to say that a 'blue' hound will have a blue-grey coat and liver-coloured lips, nose and eyerims. A 'blue' wolfhound may have this colouring but he can also be an apparently normal cream or wheaten (blue dilute has no noticeable effect on the pale coat colours) with dark nose, lips and eyerims, and may even have dark shading on muzzle, throat and ears. He can have coat colour of various shades of yellow or red, with or without brindling; grey ranging from silver to slate; or be the same colour as a blue Gt. Dane or Greyhound, having inherited a black coat together with blue dilute. His lips, nose and eyerims can vary between liver and a very dark slate grey indistinguishable from black. He may have a bluish film of hairs over ears and back, or he may not; and some 'normal' hounds in the paler colours have the same bluish film. As a very young puppy the 'blue' may have very bright blue 'speedwell' eyes but equally he may have eyes of much the same blue as his 'normal' siblings. The eye colour change of a puppy that has inherited blue dilute occurs a couple of weeks later than it does in 'normal' siblings.
The only certain way of recognising a 'blue' is by the colour of the eyes once they have changed at about eight weeks or so. Rather than try and describe the colour of a 'blue's' eyes, it is easier to suggest looking at the eye colour of a Weimaraner, or a blue Gt. Dane or Greyhound. Once seen the colour is unmistakeable, although a 'blue' can have eye colour ranging from a 'grape' colour to almost colourless, depending on whether he has inherited dark, medium, or light eyes together with blue dilute.
It is almost certain that blue dilute came into the Irish wolfhound breed through one of the Great Danes used in the early days of its resuscitation; possibly a fawn 'carrier' of the dilute gene. Thus it has by now become spread throughout the breed, even though blues themselves were not - at least officially - bred from. Inheritance is through a simple Mendelian recessive, which is one of the easiest modes of inheritance to understand.
Put simply, genes are like beads threaded on a string (the chromosome) and the strings are paired together (the dog has 39 pairs of chromosomes) with the genes situated in the same position on the paired chromosomes affecting the same characteristic. The pairs of genes are either alike (two dominants or two recessives) or opposites (one dominant and one recessive). This is really over- simplification; unfortunately few inherited characteristics are that simple and most are governed by groups of genes which are seldom simple dominants or recessives. However, there is no need to elaborate on this because the inheritance of blue dilute is that simple.
Thus there are two genes on a pair of chromosomes which control dilution. The recessive, which is for blue dilute, is given the symbol 'd' and the dominant allele (other half of the pair) which is for no dilution, is given the symbol 'D'. Recessives are always shown in lower case letters, dominants in capital letters. Where the pair is formed from one dominant and one recessive (a heterozygote) the dominant characteristic suppresses the recessive, and a recessive characteristic only becomes apparent in the animal's phenotype (appearance) when both of the gene pair are recessives (a homozygote). All dogs receiving these genes can only be of three genotypes (genetic make-up):-
Although in the body cells the chromosomes are in pairs, when the cells which form the female ova and male sperm are manufactured the pairs are separated with one half of the pair going to one sperm or ovum and the second to another. In this way, as one sperm only fertilises one ovum and an ovum can only be fertilised by one sperm, when sperm and ovum meet the chromosomes in each pair with the corresponding chromosomes in the other, so that each embryo ends up with pairs of chromosomes, one of each pair having come from the sire and one from the dam.
With simple dominants and recessives, the characteristic controlled by the recessive is only apparent in the phenotype of the dog when both halves of the gene pair are recessive, i.e. the dog is homozygous recessive, having received one recessive from each parent. In heterozygotes [where one half of the gene pair is dominant and the other recessive, i.e. a dominant has been received from one parent and a recessive from the other] the dominant characteristic will show in the dog's phenotype - in this case there will be no dilute of pigment.
Although all wolfhounds will have one of the three genotypes previously mentioned, they will be of only two phenotypes - 'blue' or 'normal'. Some of the apparently normal hounds will be, however, heterozygotes [carriers] for blue dilute and there is no way of telling from their appearance which these are.
For 'blues' to occur in a litter from 'normal' parents, both parents have to be heterozygotes [carriers] for blue dilute. It is quite possible for two carriers to be mated together and produce a 'normal' litter with no blues if none of the sperm carrying the 'd' gene happen to have fertilised an ovum carrying the corresponding gene, or none that have survived gestation. However, a proportion of the apparently normal puppies will be heterozygotes like their parents.
The various combinations of gene pairs in both parents can be expected to produce the following offspring. With heterozygotes this is only an expectation; one would require more offspring than are found in one litter of puppies to be able to determine accurately the proportions in which the various genotypes actually occur.
Blue dilute has been considered a fault in Irish wolfhounds, although it is not actually a disqualifying fault, because no such faults are mentioned in the Standard. Homozygous blue dilutes fail against the Standard because their lips and nose cannot be black and their eyes are very light.
Blue dilute is not deleterious. There is a widely-held belief that it causes physiological weaknesses and that puppies born to 'blues' will be white, deaf, and blind. It is obvious that those who believe this are mixing up dilution and the Merle factor. Merle is a dominant genetic characteristic (the exact opposite of blue dilute and not allelic to it) which is, therefore, apparent in heterozygotes (Mm). It is a lethal gene and homozygotes (MM) will be born white, blind, and deaf and may have structurally abnormal eyes.
I am not suggesting that blue wolfhounds should be bred for deliberately but only that the blue dilute should be considered in its proper context with regard to all the other inherited faults present in our breed. In this respect it is of small importance when compared to serious defects of type, soundness, health, etc. It would be foolish to discard from the breeding pool a sibling of a blue which might be a carrier of blue dilute, or to discard a known carrier, if it has virtues to offer in the way of type, longevity, temperament, conformation, and so on.
Because of its nature, a recessive is very difficult to breed out. Since one cannot tell which of the apparently normal dogs are carriers (except by test breeding), one would have to discard not only the blues but all their relations - that is, their siblings, parents, grandparents, great grandparents, etc. and all their siblings and progeny and siblings' progeny and so on, which would probably leave no breeding stock at all. All one can do is discard the recessive homozygotes (the blues themselves) from the breeding population and, although blues will still appear whenever two heterozygotes are mated together, the odds on picking a clear (homozygous dominant) to breed with from a litter containing blues are just as good as those on picking a carrier.
Back to page about the Irish wolfhound
March 9th, 2014