How do Dalmatians get their spots?
Splitting Hairs over Genetics
All human beings have the same genes and yet we all look very different to each other.
So, what is it that provides such variation?
Each of our genes has an element called an "Allele" (the full name is Allelomorph, which means "other form of", which explains nicely what they do, but this is usually shortened to Allele). Each of the alleles of each gene presents an option and only one of those options will be expressed, or manifest itself.
A really good way to think of this is to picture a coin. Imagine the coin itself is a gene and, like a coin, a gene can have more than one face or allele - like heads or tails. A gene will only show one face and so the way a gene makes us look can be very different depending on which face, or allele, is showing or expressing itself.
This is a nice simple analogy and it works perfectly when thinking about genes that have two alleles. Many genes have more than two alleles but however many alleles a gene may have, only one will be showing, or expressing itself so you can think of these genes that have more than two alleles more like dice. Just like a coin, the faces of a dice look very different to each other, but they are all part of the same dice.
A good example of this in action is hair colour. We all have a gene for dark hair, referred to as the "B" gene, but this gene can be expressed in one of two ways (just like the two faces of a coin) - the "big B" allele and the "little b" allele, and these determine whether our hair will be Black or Brown respectively.
It can be confusing sometimes when people have a tendency to refer to "the little b gene" or "the big B gene" because, strictly speaking, they are the same gene. The correct terminology would be "the little b allele of the B gene" or "the B gene expressing the little b allele" but this is a bit of a mouthful and it is easier to shorten it. Hopefully, knowing this will help to make conversations about genes a little less confusing.
Another slightly more complex example would be blood type. We all have a gene for blood type - referred to as the "I" gene - but this gene actually has 6 alleles, such as IA, IB and IO etc., which determine exactly what blood type we will be. When thinking about this gene, it is easier to think of the dice analogy than the coin analogy but the principle is just the same - only one allele, or face, will be expressing itself.
So, if you imagine that every one of our thousands of genes each has at least 2 and often more allele choices, then you can see that the combinations are endless and this is how we all end up looking and being very different to each other even though we share the same genes.
Before we explore specific genes and alleles though, we need to understand how we end up with one allele or another. The coin toss or dice rolling analogy make it sound like a completely random process of selection. However, there are some principles at play here that allow us narrow down the "odds" of what genes and alleles are going to be expressed and it's worth understanding this in more detail.
PART ONE - What are the Odds?
We inherit each gene, and its alleles, from our parents. If you gave someone a coin, you would be giving them both faces of that coin and when a parent gives us a gene, they give us both (or all) the alleles that go with that gene, not just the face/allele that expressed itself in them. So, a parent with black hair could also be passing on to us the allele that may give us brown hair.
This is complicated even further because we have two parents. This means that we receive two coins, each with two alleles - one from each parent. Now the "odds" of a particular allele expressing itself are more complex.
Having said that, there is a factor that helps to narrow things down - typically, one of the alleles will be "dominant" and the other will be "recessive". The way this works is that if a dominant allele, such as the "big B" allele, is paired with a recessive allele, such as the "little b" allele, then it will always be the "big B" allele that expresses itself.
Lets see if we can simplify this with some examples.
If both parents pass on a "B" gene with matching alleles (e.g. both being "big B" alleles) then that allele would obviously express itself and there would be a 100% chance of Black hair.
Obviously, the same applies if both parents pass on matching "little b" alleles - there would be a 100% chance of Brown hair.
If however, our Father passes on a "B" gene with a "big B" allele and a "little b" allele and our Mother also passes on a "B" gene with a "big B" allele and a "little b" allele, then the situation is a little bit more confusing. The way this is usually simplified is to draw a table and put the options from the Father on one side and the options from the Mother on the other side you can then see exactly what results exist from each possible combination. This is what it looks like...
When you display the possible combinations in this way, you can see that there is:-
- a 25% chance of Black hair
by ending up with a gene with two identical "big B" alleles (like a coin with two "heads")
- two 25% chances of Black hair
by ending up with a gene with a "big B" allele and a "little b" allele (like a normal coin) where the dominant "big B" allele will express itself
- a 25% chance of Brown hair
by ending up with a gene with two identical "little b" alleles (like a coin with two "tails")
The results of this combination are odds of 75% for Black hair and only a 25% chance of Brown hair.
If however, our Father passes on a "B" gene with a "big B" allele and a "little b" allele but our Mother passes on a "B" gene with two "little b" alleles, we would have the following options...
When you display the possible combinations in this way, you can see that there is:-
- two 25% chances of Black hair
by ending up with a gene with a "big B" allele and a "little b" allele (like a normal coin) where the dominant "big B" allele will express itself
- two 25% chances of Brown hair
by ending up with a gene with two identical "little b" alleles (like a coin with two "tails")
The balance is now very different and you end up with odds of 50% for Black or Brown hair.
The key message here is that genetics is not an exact science. We are working with "odds". This helps to explain why, even if there is apparently overwhelming history for one trait, such as Black hair, it is still possible for offspring to be born with Brown hair if there is a "little b" allele being passed down from generation to generation on both sides.
PART TWO - Spot the Dog
With this in mind, lets look at the genetics of a dog's colouring.
We have Dalmatians so I have added some specific comments about Dalmatian colouring in italic text like this but the rest of this content can be applied to any breed of dog.
There are actually only four possible colours in a dog's coat - White, Black, Brown and Red - so why is there such a wide variety of colour combinations and patterns?
Once again, the answer cannot be the genes, because they all inherit the same set of genes, so it must be in the alleles!
It is easier to think of the genes in 4 main categories:-
1. Will there be colour?
2. What colour will there be?
3. How intense will the colour be?
4. Will there be a pattern?
Let's look at them one at a time...
1. Will there be colour?
There are two genes of interest in this first category and each of them has two alleles.
The "C" gene (determines Colour or no colour)
The "C" allele = full pigmentation
The "ca" allele = no pigmentation (albino)
In the case of a Dalmatian, we want the "little ca" allele to be expressed to give the clean white coat.
The "S" gene (determines Solid or broken up by white)
The "S" allele = solid colour
The "sp" allele = piebald or random areas of no colour (white)
In the case of a Dalmatian, we want the "little sp" allele to be expressed to provide a lovely clean white coat. We pay a price for this however - the absence of pigmentation in the tiny hairs in the inner ear also prevents those hairs from vibrating properly, effectively making the dog deaf in that ear (or both ears of the pigment is missing from both). The more white there is on a dog's coat, the greater the risk that the white areas will extend to the hairs of the inner ear. This is true for all dogs with a lot of white in their coats.
2. What colour will there be?
There are four genes of interest in this category but they have an impact on each other, so we need to look at them in the correct order.
The first (the "E" gene) sets a "default" colour (which is always Red).
The second (the "K" gene) then turns on other colours that might be added to the default.
The third and fourth (the "B" and "A" genes) finally determine the actual colouring that the dog will end up with.
The "E" gene (determines if the Extension of Black/Brown pigmentation will be allowed in the hairs. If not, then the hair stays Red)
The "E" allele = Black/Brown pigmentation (eumelanin) or Red (phaeomelanin) can be produced in the hair
The "e" allele = only Red pigmentation (phaeomelanin) can be produced in hair (so there will be no Black or Brown pigmentation in the hair)
So, the "big E" allele opens the way for there to be dark coloured hair (although it doesn't determine what that colour will be). However, if the "little e" allele is expressed then there will be no dark hair - only shades of Red hair.
In the case of a Dalmatian, we want the "big E" allele to be expressed because if the "little e" allele is expressed then the result would be Lemon spots (meaning there will be no Black or Brown pigmentation in the hair, only shades of Red to Orange to yellow, which in Dalmatians we call "Lemon").
The "K" gene (is like a Key, that turns on one of the colour genes)
The "KB" allele = turns on the "B" gene (Black or Brown Pigmentation)
The "Ky" allele = turns on the "A" gene (mixtures of colours)
The "Kbr" allele = creates brindle
This is called the "Key" gene because it can only be turned to one position - either it turns on the "B" gene, or the "A" gene, or the brindle allele, but only one of them. For example, if the "B" gene is turned on then the "A" gene is not.
In the case of a Dalmatian, we want the "KB" allele to be expressed so that we can have Black or Brown spotting. Of course, the "big E" allele described above must also be expressed. If the "little e" allele is expressed then even though the "B" gene is turned on the "B/b" alleles cannot produce dark hair anyway and we will see Lemon spots. However, in this scenario, we will still see a Black or Brown nose and pads. This is because it is only Black or Brown pigmentation in the hair that is blocked by the "little e" allele. The Black or Brown pigmentation on the nose and pads will still be expressed.
The "B" gene (determines Black or Brown)
The "B" allele = black eumelanin (pigmentation)
The "b" allele = brown eumelanin (pigmentation)
In the case of a Dalmatian, this is personal taste. Some people prefer black spots and others prefer brown spots. Either colour is recognised by the Kennel Club and acceptable in a show ring.
The "A" gene (determines whether the hair will be Agouti) This word comes from a South American rodent, whose fur contains a pattern of pigmentation in which individual hairs have several bands of light and dark pigment with black tips.
The "a" allele = recessive black in the hairs
The "at" allele = Black-and-Tan (causes tricolour in Dalmatians)
The "ay" allele = Fawn (cream to yellow to red with darker tips)
The "aw" allele = Sable (black tips on cream to red hairs)
In the case of a Dalmatian, we want the "B" gene turned on and not the "A" gene. If the "A" gene is turned on then we could see "mottling" or even "tricolour" spotting.
3. How intense with the colour be?
There are 3 genes of interest in this category and each of them has two alleles.
The "D" gene (determines how much the Black/Brown pigmentation will be Diluted)
The "D" allele = no dilution of the Black or Brown
The "d" allele = dilution of the Black or Brown
Black will dilute to Blue then to Silver
Brown will dilute to Tan then to Cream
In the case of a Dalmatian, we want the "big D" allele to be expressed so that the spotting can be intense and clearly defined.
The "I" gene (determines how much the Red pigmentation will be diluted, or it's Intensity)
The "I" allele = no dilution of the Red
The "i" allele = dilution of the Red
Red will dilute to Orange then to Yellow
In the case of a Dalmatian, this gene will only matter if the "little e" allele is expressed, which will cause the spots to be Lemon. However, even if this is the case, it is still better that the spotting is intense and clearly defined.
The "G" gene (determines whether there will be gradual Greying of black or brown and paling of red hair, prior to geriatric age.
The "G" allele = premature greying
The "g" allele = no premature greying
In the case of a Dalmatian, we want the "little g" allele to be expressed so that we don't get "silver penny spotting" or greying at the edges of the spots (other than in old age).
4. Will there be any pattern?
There are 3 genes of interest in this category and each of them relates to a different type of pattern.
The "T" gene (determines how much Ticking there will be)
The "T" allele = ticking
The "Tr" allele = Roan
The "TD" allele = absence of "flecking" (Dalmatian Spots)
The "t" allele = no ticking
In the case of a Dalmatian, we want the "big D" allele to be expressed so that the spotting can be intense and clearly defined.
The "M" gene (determines if there will be a Merle pattern)
The "M" allele = Merle
The "m" allele = no Merle
In the case of a Dalmatian, this gene appears to have been bred out.
The "H" gene (determines if there will be a Harlequin pattern), the "big M" allele must also be present for this pattern to express itself.
The "H" allele = Harlequin pattern (of Great Danes)
The "h" allele = no Harlequin pattern
In the case of a Dalmatian, this gene appears to have been bred out.
Hopefully, this summary will help to you to trace the genes that have caused the colouring and pattern on your dog.
If you are thinking of having a litter of Dalmatians, then you will want...
* The "ca" allele
* The "sp" allele
* The "big E" allele
* The "KB" allele
* Either the "big B" allele or the "little b" allele
* The "big D" allele
* The "little g" allele
* and, of course, the "TD" allele
...to all be expressed, instead of any of the other possible allele combinations, which can be derived from the genes/alleles being passed down from both the Sire and the Dam, each with their own "odds" of being expressed.
That's not too much to ask is it?
PART THREE - Oranges and Lemons
The reason we started this detailed exploration into dog coat genetics was because, in our recent litter of Dalmatians, we were blessed with a Lemon spotted little boy (who we have called Lemmie).
The Sire was our own Liver spotted Sandy - and the Dam was our own Black spotted Kiki.
There seemed to be so much confusion about the possible causes of this "throw-back" that we decided to find out exactly what had happened and why.
The "C" and "S" genes
Lemmie has a very clean white coat with regular spotting so the "ca" allele and the "sp" allele are both expressed. This is no surprise as many generations of diligent breeding have more than likely bred out the "big C" and "big S" alleles a long time ago, so that the Sire and the Dam would both have passed on a gene with two identical alleles and the odds are 100% of getting this result.
The "E" genes
The next gene however is where we find the key difference between Lemmie and his parents or litter-mates (they were 3 Blacks and 2 Livers).
To have Lemon spots, Lemmie must have the "little e" allele expressed and this can only happen if, in the possible combinations that were passed to him by his parents, there is an option for a pair of "little e" alleles (like the "double headed" coin).
Obviously, if either of the parents had Lemon spots, then they would have passed on an "E" gene with a pair of "little e" alleles expressed. As we can see from the photo above, this was definitely not the case. But, it's probably worth pointing out, that even if you did mate a Lemon spotted Dalmatian to a Black or Brown spotted Dalmatian, you would not be guaranteeing another Lemon. The examples below will explain why.
In this example, the Dam is passing on a pair of "little e" alleles (because she is Lemon spotted) and the Sire is passing on a pair of "big E" alleles...
As you can see, there would have been a "big E" in every possible outcome and the dominance of the "big E" allele over the recessive "little e" allele would have resulted in the "big E" being expressed in every option.
In this next example, we will stick with the idea that the Dam Lemon spotted and is passing on a pair of "little e" alleles but now, the Sire is passing on a "big E" allele and a "little e" (he is known as a "Lemon gene carrier"), like this...
Even in this example, where a Lemon spotted Dalmatian is mated to a Lemon gene carrier Dalmatian, there is still only a 50% chance of the each of the puppies themselves being a Lemon.
So, we know that neither of Lemmie's parents passed on a pair of "little e" alleles (they weren't Lemon spotted) and we know that neither of Lemmie's parents passed on a pair of "big E" alleles (there would have been a "big E" in every combination and no Lemon spotted puppies). So, both of Lemmie parents must have passed on a "big E" allele and a "little e" allele. Like this...
This is what happened with Lemmie. Both of his parents had passed on a "little e" allele and, even though there was only a 25% chance of it happening - the option with two "little e" alleles expressed itself.
By the way, odds of 25% does not mean that 1-in-4 puppies will be Lemons. The odds are 25% for each and every puppy so the chances of it actually happening are dramatically reduced - it is actually closer to 1000:1
The "B" genes
In addition, the "KB" allele is expressed which turns on the "B" gene on in Lemmie and the "big B" allele is expressed which would have made him a Black spotted Dalmatian if that recessive "little e" allele had not got in the way. We know this because he has a Black nose and Black pads.
If the "little b" allele (Liver) had been expressed, then Lemmie would have had a Brown nose and Pads and he would have been called an "Orange" spotted Dalmatian rather than a "Lemon" spotted Dalmatian. Strange as it sounds, this would have had nothing to do with the colour of the spots themselves, which can range from Red to Tan to Yellow in both cases. It is possible to have an "Orange" spotted Dalmatian with lighter coloured spots than a "Lemon" spotted Dalmatian.
Another interesting fact is that this naming convention is reversed in Pointers - a Black nosed Pointer is called an Orange and a Brown nosed Pointer is called a Lemon.
The "D", "G" and "T" genes
Lemmie's spots are actually closer to Red than to Yellow so the "big D" allele is probably expressed.
The spots are very crisp so there is no greying, which means that the "little g" allele is probably expressed.
Finally, the "TD" allele is definitely expressed because there is no flecking, just clean well spaced spots.
So, we have our answer.
We now know exactly what happened to create our rather special little boy Lemmie, who may not be one-in-a-million but he is genetically one-in-a-thousand and we love him to bits
