Genetics of Dog Coat Color and Traits with Dr. Casey Carl, DVM

Genetics of Coat Color and Traits with Dr. Casey Carl, DVM

About the Webinar:

Dr. Casey Carl, DVM is the Associate Medical Director of Paw Print Genetics. Watch the webinar to learn all about the basics (and beyond!) of coat color genetics.

Resources:

• Canine Base Coat Color Genetic Flowchart
• Your Guide to Canine Color and Trait Genetic Testing
• Presentation Slides

Transcription

Laura Reeves [0:00] Welcome, everyone, to the Good Dog Pod podcast as well as the Good Dog Webinar Series. We have Dr. Casey Carl here from Paw Print Genetics, and we are going to cover canine modifying, coat colors, and traits—talking about the genetics of that. For people who are asking if we can hear and see you, no. The panelists are the only ones that can sort of see each other, but you guys (as Cat mentioned) can speak in the chat. Pop questions in there. We’ll get those to Dr. Carl. And we have Dr. Judi Stella, who is the Head of Standards and all the good stuff at Good Dog, who will be helping and running questions. If you have anything specific, get it to Dr. Judi. I’m here to just keep everybody in line. They gave me a whip and a chair, so we’re good to go. Some of you will have heard the podcast that we did with Dr. Carl earlier, a month or so ago. You are familiar with his fabulous presentation style. So, Dr. Carl, welcome. Thank you so much for joining us. I’m super excited to talk about this stuff. 

Dr. Casey Carl [1:14] I’m very excited to be here as well. We’ve got a few different things that we can talk about today. I’ve got kind of a general topic outline here of the things that we’re going to talk about. (If I can get this working.) There we go! First of all, we’re going to talk about an intro and some definitions, just some words that we can use to get a foundation as to what we’re going to be speaking about today, so that we’re all kind of on the same page there. We’re going to talk about a couple of types of inheritance, specifically recessive and dominant, because these two particular inheritance patterns are really important in understanding how these traits and coat colors work. As Laura mentioned, we’re going to be talking specifically about some modifying coat colors, these particular loci here (D, Em, H, I, M, and S). Basically, these coat colors are going to modify the coat colors that we refer to as our base or foundational coat colors. We’ll talk more about that here as we go. We will also talk some about traits, related to curl, improper coat, and a variety of other traits here that are important to many people. We will also do question and answer. I’m also happy to answer any questions as we go, so if you want to send some over via chat, you guys can feel free to interrupt me at any time. Dr. Stella, I’d be happy to answer any questions as we go, just so that it makes a little more sense for everyone. If they have a question, hot topic at that moment, I’m happy to answer it. 

Who am I? First of all, I probably know some of you out there that are listening today. You’ve probably talked to me on the phone if you’ve ever called into Paw Print Genetics. I’m a Washington State University graduate. (Go Cougs!) I graduated back in 2008, and I have a history in clinical medicine. I was in clinical practice for about four years in the Portland, Oregon, area. And then I joined with Paw Print Genetics in 2013. It was great for me to join as a Medical Director with them, because I saw a lot of inherited diseases in practice that were challenging and, in many cases, didn’t have treatment options. I was very motivated to join Paw Print and to be a part of moving forward with inherited diseases and how we might be able to prevent those. It’s been a great eight years there. 

First of all, we’ve got a few definitions that I think would be good for us to go over here. The first one on the list is mutation or variant. The word variant is used a lot more commonly these days than mutation is. But, essentially, this is just an alteration in the DNA code that can affect gene function. That change in that gene function can end up resulting in disease or trait. Not always. Sometimes, it doesn’t. Sometimes it may not make any change at all. In other cases, it can be completely deleterious, so that an animal wouldn’t be able to survive. But in some cases, these mutations may actually be very functional or actually still allow an animal to live but may just result in some changes to them in terms of disease or traits. 

The next word on the list is allele. Allele is a common term we use for one copy or one version of a gene, and that would come from a single parent. So, each parent is going to pass on one copy of every gene to every offspring. We often refer to that as an allele or a version of that gene. 

The next word will be genotype. Genotype is essentially the combination of both the alleles at any given location. That would be basically the combination of both genes, one from each parent that we get. We talk about genotypes frequently when it comes to genetic testing and what those might mean for an individual dog. 

If a dog has two copies or two of the same allele, we refer to that state as a homozygous state in dogs. Dogs can be either homozygous normal and have two copies of the gene; in some cases, they can be homozygous mutant, where they’ll actually have two copies of the genetic mutation. But that’s just a very commonly-used term.

And then we have heterozygous, which is basically the exact opposite in the sense that there are two different versions of the gene in this case. So, each parent would’ve passed on a different copy of the gene to the offspring. We talk about heterozygous dogs often being carriers of what we refer to as recessive diseases or traits. We’ll get into that more here soon. 

And then, lastly, we have phenotype. Phenotype is essentially that clinical or the physical presentation that we actually see that is essentially coded for by the genotype itself. Sometimes, there can be multiple genotypes that actually give the same phenotype. That is an important consideration when we think about these things. 

First, we have to think about, specifically, inheritance and how some of these traits are inherited. The first one we’ll talk about is recessive inheritance. Recessive inheritance or recessive traits are those in which a dog has to inherit two copies of the associated genetic variant. It’s important to note that that’s one from each parent. So one parent would pass on one copy, and one parent would pass on the other. An example here are these Poodles on the right side. These Poodles are essentially cream or white Poodles. This is caused by a change in the E Locus in dogs. For these dogs to have this appearance, both of the parents would’ve had to have carried that little e at the E Locus in order to produce these dogs. Dogs that only have a single copy of one of these recessive variants are considered carriers of the trait but don’t express it. So we would not expect a dog that only had a single copy of these to actually show it, but if bred with another dog that also had the same mutation, then they could produce dogs with that trait. 

Quite often, especially when we talk about color specifically, the recessive alleles are commonly notated with a lower-case letter. In the case of these dogs here, this kind of cream to white color—these dogs would typically be expected to be e/e. That little e is notating the recessive version of this gene. Dogs that are carriers would have a capital E and a little e. The capital E is dominant to the little e, so that means that we won’t actually see that cream, apricot, or red color in this case unless this dog were to be bred with another dog that carried that. 

What does that mean? If we take a look at what we call a punnett square (and you may have seen this square here on the right if you’ve ever taken a biology course that had any genetics in it), this is a very useful tool to help us understand if we bred two dogs together, how their specific genes or locus in this case might actually be passed onto offspring and to understand the ratio that we may get from a particular pairing of dogs. In this case, we have a situation where dogs are carriers of a recessive trait, meaning they have one copy of a recessive trait, but neither of these dogs would actually show that recessive trait, because it requires two copies for them to be shown. If you happen to breed two carriers of a trait together like this, and then we use this fancy punnett square here where we have the capital letter here indicating the dominant version of the gene and then the recessive version here with the little a, we can actually kind of extrapolate this out. Pulling this into this square for each of these dogs. What it does is it starts to give us a picture as to what we would expect from breeding these two dogs together. Let’s say both of these dogs carry cream or apricot color. What we would find is about one out of every four puppies would have two copies of the regular version of the gene (these dogs would be normal or would not have the specific trait as well at all in their genome.) About two out of four (50% of the dogs) would end up having one copy. These dogs would be carriers of that particular trait but would not be showing it. And then, lastly, about 25% of the puppies would end up actually getting two copies of that and actually expressing that particular trait that we were looking to get. Now, if one of these dogs actually happened to have the trait (so, say, one of these carriers actually had two copies and actually had the trait there), then we would actually get more dogs—about double the amount of dogs—that actually expressed that particular trait. What we know is that both parents at least have to carry that in order to get a recessive trait. 

The other common method of inheritance that we talk about would be dominant mutations. I have a little merle dog here that we see. Merle is one of the coat color patterns that is dominant, meaning it only requires one copy of the associated mutation to actually produce this pattern. We’re going to talk a lot more about these here a little bit later, about merle at least. But in general, dominant diseases do only require that one copy of the associated genetic variance to develop it. In this case, most dominant alleles (as I mentioned earlier) tend to be notated with capital letters. So in the case of a merle dog, you’re going to have a little m and a big M, and that big M is indicating the dominant mutation, which is responsible for producing this merle coat color that we see here in this dog. 

So, very similar to what we did with the recessive traits, now we’re showing a dominant inheritance pattern here. This dog expressing whatever that trait is, and we have a dog here that doesn’t have that mutation and is therefore normal or clear for that particular trait. We’ve got to set up here again. The normal dog being on top here, and the dog wit that dominant trait on the side. As we go ahead and use our punnett square again (as we did previously) and pull in these copies of the gene, we will find out that in this particular case, about two out of every four (or, half of the dogs—50%) would actually end up as normal or clear and not have the trait. And then about 50% would actually end up with it. There is a little bit of a concerning thing that we sometimes deal with in dominant mutations (we’ll talk about this in merle, in hairlessness, as well as natural bobtail here in a little bit), in some cases, if you breed two dogs that both have a dominant mutation together, any of the dogs that happen to get two copies of that dominant mutation—they can suffer from a deleterious issue of some sort. In the case of merle, we’ll talk about double merle dogs that inherit two copies of that mutation. But if we follow the same pattern here with the punnett square, and we go through the same type of process here, we’ll find that if we breed two dogs together with the dominant trait, about 25% of them will actually not have the trait at all. About 50% will actually express the trait. And then there will be about 25% of the dogs that may have a deleterious effect because they inherited two copies of that dominant mutation. In the case of merle, that would be the double merle appearance. In the case of some of the other traits we’ll talk about today, it can end up resulting in in utero death, so you end up with smaller litter sizes if some of the puppies end up getting two copies of these. We’ll talk about that more when we get to those particular traits. 

We’re going to talk about some modifying coat colors. Those modifying coat colors modify the foundation or base coat color that is determined by these four loci that are outlined here in this big graph. They’re the E Locus, the K Locus, the A Locus, and the B Locus. This looks quite complex, but it’s essentially showing different directions or different ways that these loci can actually influence color in dogs. We can see at this top one here that we’re talking about the E Locus. If a dog is e/e, it’s going to be yellow to red and cannot produce black or brown hair pigment. If we’re going down the other pathway, if a dog has a capital E at all, then we have to go down this other pathway to figure out more of the foundational coat color. I did talk about some of these foundational coat colors (at least a cursory look at them) on the Good Dog Pod with Laura Reeves back in episode 18, if you want to check it out. If there’s interest, we may dive into this further. This is kind of the first of this type of presentation that I’ve done with Good Dog. We can go back and maybe take a more in-depth look at some of these foundational coat colors in the future, if there’s interest out there. Since we already kind of covered it on the podcast, we’re going to step forward here and talk more about the colors that modify those particular loci. 

Today, we are going to talk about the D, the Em. We’re going to briefly discuss the harlequin Locus, which is found in Great Danes, and then we’re going to talk about the I and the S Loci as well. This is my little critter down here on the bottom. His name’s Spike. We had to give him a tough name because he’s less than ten pounds, but depending on the day, I also sometimes call him El Terrible because he looks real nice and he’s really cute, but he’s got an attitude much bigger than his size. Occasionally, there could be people on the receiving end of that. If he were a human, he probably wouldn’t be allowed to be in public very often. But we love him all the same!

As I mentioned, these genetic variants will modify those base foundational coat colors. The first one we’re going to talk about is the D Locus. The D Locus is also referred to as the Dilute Locus. It’s located in what we call the MLPH gene in dogs. There are two alleles (or two versions of the gene) that we test for or that we’re looking for, one of which is the capital D, which is the dominant version of the gene. That is non-dilute. This is a recessive trait, so dogs that get two copies of the little d will have a diluted coat color. What that means is that the coat color that they would’ve had otherwise (determined by those foundational coat colors) essentially takes what color they would’ve had and dilutes it or makes it a much lighter color. As you can see down here in the bottom, I’ve got these three different dogs. I’ve got a dog here which is essentially a dilute black. It almost looks black in this picture, but it’s actually a very dark gray or charcoal appearance often referred to as blue in many breeds. (This Frenchie here.) Dogs that are d/d (all of these dogs) also have changes to their nose and foot pad color, which are also dilute in this case and will often be similar in nature to their hair color. In the middle here, we have a dilute brown dog, which is essentially what all Weimaraners are. This dilute brown, often referred to as silver or gray, depending on what breeds you’re talking about. And then over here, on the far right, we do have a dilute fawn dog. I was trying to find a version of a dilute yellow, like we see in some breeds, but I couldn’t find it. This dilute fawn is also something that we see quite commonly in a lot of breeds. You notice how the nose color is more of a gray. This mask that we have on the face is also more gray, and there’s almost a gray hue to the dog in general that we see in these dilute dogs. 

It is really important to note that this is not the cause of progressive graying or fading. This is something that we see quite commonly in breeds like the Poodle. One of the people that are attending today, they had sent in a question regarding a graying gene in dogs. We don’t know what the graying gene is. It is very common in some breeds. It is very common in Poodles. The person that was asking this question was specifically asking in Portuguese Water Dogs. I’m not familiar with it being found in Portuguese Water Dogs very often. It wouldn’t surprise me if it was present in there, but at this time, we don’t actually understand or know the genetics behind that progressive gray at this time. This is an independent cause of a very similar appearance. The major difference is the dogs that have a D Locus variant that is causing dilution—if they’re d/d—these dogs are actually born with that coat color dilution, whereas the progressive graying or fading, these dogs will be born with their typical dark color (black or brown) and, as they age, they’ll actually see this color change as they go forward in age. There are actually multiple genetic variants at the D Locus. We are currently testing for two of them at Paw Print Genetics. They go by the d1 and d2 allele. The d1 is the one that’s responsible for coat color dilution in a very wide variety of breeds, particularly the Weimaraner, French Bulldog—there’s a lot of breeds that have this. But this i the one that’s found in the Weimaraner and a lot of other breeds. And there’s a second one that we’re also currently testing for. It’s been found in the Chow, the Thai Ridgeback, a few other breeds. I believe it’s potentially found in some of the Pitbull or bully breeds. The important part is, though, that both of these mutations are found in the same gene. If a dog happens to inherit one copy of either of these mutations from both parents (as long as a dog gets either d1 or d2 from either parent), as long as they get those, they will have a dilute coat. For example, a dog can have one copy of d1 from one parent and actually get the d2 mutation from the other parent, and they’ll still have coat color dilution. It’s still in the same gene, even though they don’t necessarily have two copies of the exact same mutation. In this case, since these mutations are in the same gene, they still will produce a coat color dilution. This is a phenomenon that is often referred to as compound heterozygosity in dogs. Big fancy name for saying that, essentially, since these are in the same gene, they can function similarly in terms of the trait that they would cause. 

Dr. Judi Stella [19:07] Can I interrupt here? There was a question: Do you know which of those variants is associated with the coat color dilution alopecia? And then we also had a question about blue in Afghan Hounds. Do you know which variant it is?

Dr. Casey Carl [19:29] You know, I would have to look at Afghans. I’m not sure if they’re some of the ones that would fade into the color. If they do, then it would not be this. If they are born a blue color, then it would likely be due to one of these variants. I would have to look and see how that typically manifests i the Afghan. In terms of the alopecia that you mentioned, unfortunately, there’s not a specific genetic mutation that’s known for that. We know that dogs that are dilutes can develop color dilution alopecia. We don’t fully understand why some dogs are more prone to it than others. It quite often starts as a progressive hair loss on the trunk. It does progress and, quite often, it can affect a large portion of the dog. It has to do with the way that melanin clumps in the hair of these dogs. It ends up causing the hair to fracture as it emerges from the skin. Interestingly, tan areas are unaffected, so if you look at these pictures (it’s a little hard to tell in these pictures) but this is a Doberman that’s in these pictures, and the tan areas down here around the leg actually do have tan hair on them, down here—whereas the other portions of the dog have actually lost a large portion of their hair, and it’s very thin here in these other areas that are not tan. This is a very common thing that we see. Sometimes this condition can also be associated by secondary bacterial infection of the skin, particularly in the hair follicles, referred to as folliculitis. Sometimes these dogs need to be managed long-term with that. Unfortunately, as I mentioned, we don’t know the specific genetics behind why one dog would inherit or develop this alopecia whereas others won’t. Some breeds seem to be a lot more likely to develop the alopecia. For instance, Dobermans are one of the breeds that seem to have a very high likelihood of developing this alopecia if they happen to be dilute, whereas other breeds like the Weimaraner don’t seem to be quite as commonly affected. They can be, but they are much less likely to be than some other breeds. There are probably some other genetic factors that play a role in this that we just don’t quite know yet, as to how that happens. Did I answer both of those questions, Dr. Stella?

Dr. Judi Stella [21:39] Yes, thank you very much.

Dr. Casey Carl [21:41] I did have another question that was sent in early to you, asking about blue puppies and how to avoid them. Essentially, this comes back to breeding again: not breeding two dogs together that both carry these D Locus mutations (the little d locus). That would be the most important thing. So one of the dogs would need to be D/D in order to avoid producing those blue puppies. 

The next one on our list here is the Em Locus. It’s in the MC1R gene. It’s often referred to as melanistic mask. This is a black or brown mask that we can see on a lot of dogs. It’s most commonly seen on fawn or sable dogs. It is a dominant trait, meaning that it only requires one copy of that Em variant to actually produce this mask, but they do have to have other conditions met in order for the mask to actually be seen in them. It’s not really visible in a solid black or brown dog, or in the case of a dog that has white all over its muzzle; it may actually mask where the mask will be. It will prevent you from seeing the mask on the face. For instance, on this picture here on the right with the Saint Bernard, there’s some other genetics going on here that produce this white color on the face. This white is essentially a lack of pigment in this region. But if you notice just outside of the white, on the Saint Bernard, you can actually see a mask there. So this dog technically has a mask, but it’s not going to be visible here where the white is on this dog, because there’s simply no pigment there at all—whereas this dog here on the left is a fawn-colored dog that does have this mask. It’s very obvious to see. This is the cause of the mask that we see in a lot of fawn-colored dogs. Really common in fawn pugs, fawn Great Danes, and other breeds. Sometimes you can actually have dogs that have masks that would’ve had tan points. For instance, the color pattern that we would see in a Rottweiler or a Doberman—some other breeds also have that same coat pattern. A lot of breeds do. If those dogs have masks, in some cases, if their mask happens to be incredibly large on their face, sometimes it will actually even cover up the little tan markings that they have above their eyebrows. Some dogs that technically have tan points, if they also have a mask, they may not have the tan marks above their eyebrows like other dogs do that are also tan-pointed. 

It’s really important to note as well that this mask cannot be seen in cream, apricot, or red dogs. Or dogs that are e/e at the E Locus. Because dogs that are e/e at the E Locus—they actually cannot produce black or brown in their haircoat. For that reason, you would not see this mask in them, even if they had the genetics for it, it would not be able to be seen in that particular dog. So you’re really only going to see this most commonly in sable or fawn dogs. Occasionally, you’ll notice (as I mentioned) the tan eyebrows, essentially missing in some tan-pointed dogs if they happen to have a very large version of the mask. For the most part, it’s going to be seen in fawn and sable. 

The next thing we’re going to talk about here goes by the I Locus, or intensity locus. This is somewhat of a new mutation here. I actually got a question about this ahead of time. Someone was asking: Is it true that cream-colored dogs are e/e? Indeed they are! Cream-colored dogs are e/e, but there’s definitely some variation in dogs that are e/e and what colors they can produce. They can be nearly almost all white, like this white Shepherd here in this picture, all the way up through a fox red color that we can see in Poodles. We can see it in some “yellow” Labradors. But that fox red is considered a variation on that yellow theme, there. But we do have a mutation location known as the I Locus that is actually responsible for taking e/e dogs and making them much more white, like this dog is here. It is the cause of this white appearance in white Poodles, white Shepherds, and a host of other breeds. It’s definitely not the only cause of white. There are other genetic mutations which cause white out there, specifically more of an extreme white appearance, like these dogs have. Unfortunately, some of these mutations are also associated with deafness and issues. This particular mutation (as far as I’m aware) is not associated with deafness. It has not been associated with that to my knowledge, but can be really useful if you want to get that very light or white color in some lines of dogs.

Right now, at Paw Print Genetics, we are not currently offering it as a stand-alone test, but we do have it listed as one of our tests on our genetic screening product, The Canine Health Check, that you can find on caninehealthcheck.com. We do plan to bring it to Paw Print Genetics as as stand-alone test in the future. We just don’t have it available right now. But as I mentioned, dogs that inherit two copies of this mutation along with two copies of the little e will have this white appearance.

A very hot topic (and a somewhat controversial topic at times) is merle coat color. That’s next on our list here. Merle is caused by a mutation in what we call the PMEL gene. There are two basic alleles to this, for this gene here, one of which is the actual merle variant (which is notated by capital M, because it is a dominant mutation) and then there’s dominant to non-merle. But merle’s a little unique. Merle is caused by a piece of DNA that’s been inserted into this gene called PMEL gene. This piece of DNA that’s been inserted in there is very unstable, from generation to generation. It’s very unstable when a cell has to replicate itself during development, for example. So when a dog is developing all of these cells and they have to be replicated in order to produce more cells for the dog, they actually have to reproduce all of the genetic material for that dog in each and every cell, even if it’s not necessarily expressed in that cell. All of that material is here. When it comes to merle, when the body is trying to replicate this particular area of the genome where the merle mutation exists, it’s not very good at doing that. It ends up resulting in the size of that merle mutation changing to some degree. The change in the size of that mutation is what’s responsible for giving us the very wide variability in appearance that we see in merle dogs, all the way from dogs that have a copy of the merle mutation that don’t look merle at all, all the way up through a dog that has more of a harlequin or (in this case) looks more like a classical appearance here. But dogs that would have a harlequin experience, that would have white separating these areas of full pigmentation. Merle is defined as, essentially, random regions of fully-pigmented hair separated by either dilute regions (this gray, dilute color like we saw with the D Locus that looks very similar to that) or in some cases white, which we would see in harlequin-colored dogs. As I mentioned, the size of that M Locus mutation is associated with the overall differences in merle appearance. 

Here we’re showing that we’ve got four different groups that, at Paw Print Genetics, we’ve essentially grouped all of these dogs into. There are other schemes out there. There are some other scheme that separate these into additional groups, but we found that these four groups tend to give us most of what we’re needing to know about these dogs. The boundaries between these groups are not really definite boundaries. There are definitely dogs that can have a size of a merle mutation which falls into these other groups and these numbers here are just representing the number of base pairs that we find in this particular mutation. This gives us the overall size here. Classic merle dogs, like this dog here that has the M267—this appearance here tends to fall in this 265-269 range. However, as you notice here, the dog directly above it is also a 267, and it doesn’t have quite the classic look. It almost looks a little bit more like a diluted look or an atypical look, where it doesn’t have fully pigmented regions that are quite as obvious as this dog. So this is just showing that there is some variation in each of these sizes, but in general, they tend to fall out into these general groups: cryptic, atypical, classic, and harlequin. Harlequin, like I mentioned, is a little bit of a unique color that is defined here by dogs that have this fully-pigmented region but white in between all of the colored portions. These dogs can also end up having a pattern here that we refer to as tweed or patchwork, where they may have different shades of that colored portion in there but then they would have white. Now, it’s important to note that this is different than Great Dane harlequin that we see. (I’m going to talk about that here in just a moment.) There’s actually a different genetic underpinning for harlequin that we see in Danes, in addition to merle, that is really important for them. (We’ll talk about that here in just a moment.) 

Merle breeding does have a huge responsibility when it comes to breeding because breeding two merle dogs together can end up resulting in disease or in a situation that we refer to as double merles, sometimes referred to as lethal white or a variety of other things. It’s sometimes referred to as double dapple in Dachshunds because that was the terminology that tends to be used there in them. Dogs that inherit two copies of a functional merle mutation may end up looking like these dogs. By functional I mean that the size of the mutation is above the cryptic merle size. The dogs that inherit very small versions of the merle mutation may not actually appear merle at all. That can be quite confusing. We often refer to those dogs as cryptic merle dogs. Where we get concerned about breeding merle dogs is that sometimes these cryptic merle dogs can actually have the size of their merle mutation enlarged to some degree. If their merle mutation enlarges and that gets passed onto their offspring and then that offspring also inherits a larger version of the merle mutation from the other parent, then they might end up like these dogs here, which tend to be nearly all white. They quite often will have hearing or vision deficiencies. In some cases, they’ll actually have developmental abnormalities of the eye, like in this Great Dane here. This Great Dane actually has an underdevelopment of the eyes. I think the Dachshund may actually be showing some of that as well here. Typically, these dogs are not going to be visual. Over here on the right, we’ve got an Australian Shepherd that looks like it probably is able to see, but it could potentially be deaf. It’s very common that these double merles are deaf. It can be quite, quite challenging for people, obviously. It’s really important to not breed two merle dogs together. 

At Paw Print Genetics, we’ve taken the stance that we recommend not breeding two dogs together if they both carry the merle mutation, regardless of what that size is. I know that there are people out there that will argue in favor of actually breeding cryptic merle to merle dogs. It’s just not something that we have felt comfortable with recommending, because there is this rare chance that possibly these dogs could end up resulting in double merle dogs, if these cryptic merles have that enlarged. That’s our current take on this. We would not recommend breeding two merle dogs together, regardless of whether one of them is cryptic merle or not. It just would not be recommended. 

As I mentioned, Great Danes can also have a harlequin coat color appearance. They have a different mutation at what we refer to as the H Locus that they have to inherit along with merle, in order to actually get their appearance. Both of the variants are considered dominant in the sense that it only requires one copy of each of these to actually give this color. This harlequin Dane down here on the bottom has one copy of merle and one copy of the harlequin variant that is unique to Great Danes. That’s what gives them this great color here. The reason that it’s important to consider testing for this in Great Danes (in the H Locus in Danes) is that some dogs that carry harlequin—that have one copy of harlequin—may actually appear mantle. So this dog that we have up here (taking a time out on this chair here)—this dog could actually be a carrier of harlequin and we wouldn’t know it by simply looking at that. The reason that’s concerning is if you breed two dogs together that have harlequin (just like we talked about with merle)—they don’t actually produce a disease that allows them to live, but they will typically pass away in utero. So two Great Danes—if we breed them together, if they’re both carrying harlequin—they will pass away in utero. It will typically end up resulting in 25% smaller litter sizes, because those dogs don’t ever make it to be born. It’s incredibly important to not breed two harlequin Danes together, because not only are they carrying harlequin, but they’re also carrying merle together. This is a situation where we could get into these double merles. No merle dog should be bred to an actual harlequin Dane. We wouldn’t want to breed two merles together. We wouldn’t want to breed two harlequins together. Basically, the ideal breeding—if we want to keep our litters large and we want to try to get harlequin Danes—is to breed a mantle dog (like this one, that actually carries the harlequin variant) to a merle dog. In that case, about 25% of the litter would be harlequin. Another 25% would be merle as well. The remaining 50% would be dictated by the other areas of the genome, in terms of their colors. This would be an ideal way to bread harlequin Danes without having to deal with any in utero death or without being concerned about the double merle situation. This, I think, can be very helpful for breeding these dogs. 

Next one we have here on the list is the S Locus. The S Locus is an important genetic variant in a lot of different breeds. It’s often also referred to as the spotting locus. It’s found in the MITF gene. There are two basic alleles that we talk about here. The Capital S for no spotting. That is typically dominant to the parti or the Sp. It’s usually dominant to them, because there are occasions where perhaps dogs can actually have some semi-dominant traits associated with one copy of this mutation, meaning that if they inherit one copy of Sp, there are occasionally dogs that might show a random white spot somewhere on the body or something like that, related to that. It’s not very common that that happens. Most of the time, it does require two copies of Sp for a dog to get that white, and when they do, they would be considered what we call parti in Poodles, piebald in a lot of other breeds—where basically greater than 50% of the dog will actually be white. The colored portion will be determine by the other areas of the genome, but they would typically be more than 50% white. This is a very random pattern of white on the dog. We have other causes of white which are not so random. We also have other causes of white (as I mentioned) that can cause an extreme white appearance, or other causes of white that we don’t know yet. This is just one cause of white that we really do have an understanding of. It is a very common cause of white in a variety of breeds, including these three breeds down here. As I mentioned in the Poodle, we call it parti. Not something we typically would see in the showering, but you definitely do see it out there in Poodles. And these other two dogs also showing that very similar parti or piebald appearance.

It is important to note that there is another very important cause of white in dogs that is not caused by the S Locus. However, the S Locus can actually modify this appearance. This is referred to as Irish spotting in most breeds. It can also be referred to as abstract in Poodles. This is the white. It can be a variable amount of white. In some cases, it’s only seen just on the chest or the toes. This is often referred to as Irish white spotting. It’s the white that we see on the chest, on the tips of the toes and the tail. Sometimes it comes up between the eyes, like we see here in this Bernese Mountain Dog. In some breeds, it comes up around the collar. That’s commonly seen in the Australian Shepherd. But it is isolated to only these areas. This would not be considered parti, because it’s not random around the dog. So this is a different color. It is the cause of the white that we see in tricolor dogs (like both of these dogs). That is the white. Now as I mentioned, it’s not caused by the S Locus or the Sp variant. That’s not why Irish spotting is there to begin with. But if a dog does inherit Irish spotting and it also gets one copy of parti (the Sp variant), then the white that we have in all of these areas tends to be expanded to some degree. So the white that we would see on the chest, the toes, the tip of the tail—all of that would be expanded out and they would tend to have more white in those areas. It’s not the reason it’s there to begin with, but it can play a role in causing it to be more pronounced. The specific genetic variant for the Irish spotting (this pattern) is not known at this time. So we can’t necessarily predict that. But, in some cases, if they get it together (as I mentioned) with the parti variant, they will have more white on them in those regions. I know we’re talking mostly about purebred dogs and some mixed breed/hybrid dogs. Sometimes people will use this to their advantage to try to get more white in these regions in some breeds. 

Somebody had sent in a question beforehand asking about tuxedo markings or abstract marks in dogs. They had asked if it was caused by parti coloration or if there is another gene involved. As I mentioned, there is another gene involved. The Sp can definitely play a role in causing tuxedo or mismarks in dogs by causing that white to be more pronounced, but it’s definitely not the only factor involved there. We have this other unknown factor there that we’re still dealing with in order to try to get that appearance. 

That is a rundown of the colors. I want to check in with Dr. Stella here to see what, if any, questions we had regarding those, so we can address those.

Dr. Judi Stella [40:22] We did have a few questions. If you don’t mind, let’s do the colors, and then we can get back to the traits. Just starting from the white: What if there is only white on the chest (not on the toes and the tail), is that still Irish spotting?

Dr. Casey Carl [40:39] Yeah, it is. It’s still considered Irish spotting. It’s highly variable how much white they will get. You can find it just on the chest. Sometimes it’ll be just on the toes. It can be variable, and we don’t have a great way of predicting that yet, as to where it will necessarily be located. 

Dr. Judi Stella [40:56] We have a question about (specifically in Aussies): Which gene causes excessive white? 

Dr. Casey Carl [41:03] We don’t know yet. It’s definitely out there. It is one of the causes of excessive white is also associated with deafness as well, so that’s a big concern in some breeds. But at this point, we just don’t know. 

Laura Reeves [41:31] Judi, I’ll leap frog with you so we can do this together. The one that I thought was really interesting, Dr. Carl, is Lou asked: In Eurasiers, the coat color seems to have evolved throughout their lives. Is there a genetic explanation for morphing coat color?

Dr. Casey Carl [41:59] Not yet. Potentially in the future, there will be, but at this time, anything with that type of changing, we don’t really have a good grip on yet. 

Dr. Judi Stella [42:04] If a dog is Em/Em (big E, little m twice), how do you breed away from the melanistic mask?

Dr. Casey Carl [42:13] To start with, you would have to find a dog that doesn’t carry it at all and breed the dog that has two copies of mask to that dog. In that first generation, you would get an entire litter that would still have mask. They would have one copy of it. But since it’s dominant, they would still be able to produce a mask if they happened to be fawn or sable. It would take you two generations to get to the point where you would stop producing that mask. So if you took one of those puppies that had one copy and you bred it back again to another dog that was clear for mask or didn’t have it, then you would start getting into a situation where you would start getting some dogs without the mask. So it would take a couple of generations to get there, but you could definitely do it by breeding back to a clear dog. 

Dr. Judi Stella [42:55] Somebody has a red fawn dog with a black mask. The question is: Is that dog really sable?

Dr. Casey Carl [43:02] Yeah, so fawn and sable genetically fall into the same category, at least from what we can test for right now. The A and the K Locus play a role in creating a fawn or sable. There are probably some other genetic factors that play a role in individual breeds as to whether they actually become fawn or sable, but technically genetically they’re very similar at the A and K Locus. Yes, I would still consider that dog to be a fawn or sable. The actual light color of the fawn or sable can vary in the exact same way that the E Locus can vary. The light color in the fawn or sable (or even the light color in the tan points) can vary in the exact same way that dogs that are e/e can vary in color, almost from that pure white up through that fox red. We don’t have that fully worked out yet, as to how that all works, but you can still see that large variation. It depends on the breed. It depends on the genetic background of the individual, so there’s some other factors there that we don’t know yet. 

Dr. Judi Stella [44:01] So what can you tell about the rufus gene and how can we tell if a dog is a carrier?

Dr. Casey Carl [44:07] We don’t yet. Nobody has determined what that is yet. There has been a fairly recent discovery of a mutation that is believed to perhaps enhance the intensity of some of these colors. I’ve read over the paper a little bit. Nobody is offering it currently, and I’m not sure how widespread that specific mutation might be, in order to explain some of these things, but it could explain some similar phenomenon as the darkening—but, at this point, as far as I’m aware, there’s not a specific mutation associated with that rufus characteristic, which is often talked about in Poodles where they actually become more dark in their red color as they age. Right now, at this time, as far as I’m aware, there’s not a specific mutation that can be tested for that would identify that. 

Dr. Judi Stella [44:53] Somebody asked about cryptic merle in Chihuahuas. Is the cryptic merle the same in all breeds?

Dr. Casey Carl [44:57] Yeah, it is. Any breed or any dog that has merle in their line potentially could have cryptic merle as a phenomenon in there. In order to test for cryptic merle, you just have to do a standard M Locus test. With us at Paw Print, we actually will size it and tell you what you’re looking at and if a dog is a cryptic merle, we would expect that size to be very small, on the small end of the scale. 

Dr. Judi Stella [45:23] I think you touched on the graying gene, we just don’t have a test for that, correct?

Dr. Casey Carl [45:27] We don’t yet. It is different than the D Locus, as I mentioned. The D Locus is responsible for producing that gray or dilute appearance in dogs from the time they’re born, whereas that progressive gray or fading is going to be something that would be seen after birth. We don’t have the genetics behind that one that causes the change after. 

Dr. Judi Stella [45:47] How does sable arrive, and what are the modifiers?

Dr. Casey Carl [45:52] Sable, as I mentioned, is the same as fawn. If we were looking at it from the foundational coat color perspective, the K and the A Locus both play a role in that. How it works with the A and the K Locus—the way I think about it—is the K Locus is essentially the on/off switch for the A Locus. And the A Locus is what actually codes for fawn, sable, or tan points in dogs. In order for the A Locus to actually be turned on, though, a dog would have to be what we refer to as Ky/Ky at the K Locus. If a dog is Ky/Ky, that turns on their A Locus. If they have the appropriate genetics at the A Locus, then they would be either fawn or sable depending on the breed or their genetic background. Fawn or sable is typically coded for by Ay at the A Locus, and Ay is the most dominant of the various alleles that can be present at the A Locus. There are actually four different alleles that we look at at the A Locus. Ay is the most dominant. So if a dog is Ky/Ky, it turns on that A Locus, and if they also have one copy of Ay, then we would expect them to fall somewhere in that fawn to sable color pattern. As I mentioned, we don’t really understand fully why some dogs would be more towards sable and more towards fawn in other dogs. There are some variants there that we don’t fully understand yet. 

Dr. Judi Stella [47:11] Is that where the clear sable falls in?

Dr. Casey Carl [47:14] Yeah. They can refer to it as a clear sable or, in some cases in dogs that have a sable appearance that’s more red (like, for instance in Dachshunds, it’s referred to as shaded red), there can be potentially some variation on that theme in all breeds. They have some variants there. The underlying genetic variants are very similar in a lot of breeds, across breeds, but there is some variation on the nuances of each of these colors for each breed, because each breed does have their own genetic background. All of this background is still what we don’t yet know in many cases, so there can be some slight variability to these themes, depending on the breed.

Dr. Judi Stella [48:59] So we have a few more questions about white spotting. What about white spotting on terriers?

Dr. Casey Carl [48:07] Depends on what that white looks like. As I mentioned, the S Locus is really the only one that we can technically test for, so if it’s a random smattering of white on the dog, I do know that in a variety of those breeds, the S Locus does play a role in the piebald appearance of those dogs. If the white is isolated to just those areas of the chest, toes, tail, and perhaps around the color (as we mentioned earlier) that would fall into that Irish white spotting, which would not be something that we could test for. As I mentioned, the white is tricky because there are some unknown variants out there that could cause white, potentially, and we wouldn’t be able to know. But if you tested that dog at the S Locus, if it had white on it, that could give you an indication as to where they’re getting it. Again, if it’s in those areas (isolated to the chest, toes, tail) that is probably going to be more like that Irish spotting.

Dr. Judi Stella [48:57] Did we touch on the brindle? Because I know we had a couple of questions that people had written in about beforehand. 

Dr. Casey Carl [49:10] Brindle is interesting. We know what the genetic mutation is that causes brindle, but it is difficult to test for. At this point, as far as I’m aware, there’s not anybody that’s actually actively testing for it out there. It is a mutation that involves the K Locus. All brindle dogs will come up as what we refer to as Kb/Ky at the K Locus when they’re brindle. However, not all Kb/Ky dogs are brindle. It’s just that when a dog is brindle, that’s always the way that the test result shows. There essentially are both components of the Kb and Ky allele within the brindle mutation, so both are seen when we see these dogs. Brindle can be isolated to just the points on a dog, or it can be spread across the whole dog. What determines that is, again, the A and the K Locus. So if the dog would otherwise have been fawn or sable and it also inherits brindle, that fawn or sable dog will actually have a full-body brindle on them, whereas if the dog would have otherwise just had tan points (and they also inherit brindle), the brindle will be isolated to just the tan-pointed regions of the dog when they get that. So that’s why some dogs only have them on the points is because they are technically a dog that also codes for tan points. That’s the only place that that brindle will show up. Unfortunately, as I mentioned, at this time, we don’t have a way to really test for that. Dogs that are brindle in actuality can have two copies of brindle or they can actually have one copy of the brindle mutation and one copy of Ky at the K Locus. Either way, when we do the genetic testing, they’re all going to come out as Kb/Ky on testing. But we kind of understand how this is inherited. You can’t tell by looking at a brindle dog whether they actually carry two copies of brindle or one copy of brindle and whether they would pass it on to 100% of their puppies or only 50% of their puppies. It would require breeding to really know that right now. 

Dr. Judi Stella [51:10] That’s interesting. How about we do two more? Somebody asked about the genetic make-up of Dalmations, which is interesting. 

Dr. Casey Carl [51:17] Dalmations, yeah! I don’t know that that’s actually known at this time. In addition to that tick marking in a lot of breeds (like we see in the Pointers and things), that white that we see there, that pattern, is not yet understood from a genetic perspective. 

Laura Reeves [51:32] Real quick as a follow-up to that, I saw a couple of questions on this: roaming, ticking, spotting. Is that falling in that same category?

Dr. Casey Carl [51:35] It is. I’d have to go back now and look on the Dalmation. I think there are some genetics behind that that have been identified. In terms of the roaming and any of that type of tick marking, none of that has been worked out. So those are still a little bit of a mystery to us, about how that works. 

Dr. Judi Stella [52:03] Okay, and one last one about merle: Is there any way for merle to hide in e/e dogs in a specific breed for decades without expressing in deafness, blindness, or other health issues?

Dr. Casey Carl [52:27] Yes, there is. Any e/e dog could also technically be merle, and you’d have no idea. The reason being that e/e dogs cannot produce that black or brown in their hair coat, so you can’t see the differentiation which occurs with the merle variant. Yes, that could happen for a very long time. As long as two e/e dogs weren’t bred together (both carrying merle), then you may never get a double merle dog. It would be required that both of those dogs do carry a functional version of merle in order for that to be the case. Yes, it’s very common that that happens where the e/e can mask any brown or black color. Things like that happen quite commonly in a variety of breeds, including the Golden Retriever. Many Golden Retrievers actually technically have the genetics for tan points. You would never know it by simply looking at them, because that black or that tan color can’t be differentiated. 

Dr. Judi Stella [53:12] Interesting. 

Laura Reeves [53:17] We have to transition now to traits because we could spend the next six days talking about color and picking Dr. Carl’s brain. 

Dr. Casey Carl [53:42] That is great. I’m glad people have questions, because that’s always fantastic. We’ll move into the traits here a little bit. We may have some more time here at the end. If we want to get back to some of these, that would be awesome. This is a great little graphic that I got from this paper here by Cadieu in Science back in 2009. Essentially, this paper was showing that there are three major jeans that play a role in the overall appearance of the dogs in terms of their hair quality. The FPO5, the FPO2, and the KRT71 gene. We’ll talk about all these here and how they influence all of these general appearances that we get in our dogs.  The first thing we’ll talk about is the C Locus and KRT71 gene. It also goes by the curl locus. There are essentially two alleles here. One that we call the CuC (with that superscript C there). That is coding for curl. You’ll notice here in these traits as well that they don’t follow the general conventions of the capital letters versus the lower-case letters like we do with the colors. These tend to have completely different names for the two different alleles. In this case, for the straight hair, we just do a straight Cu without the superscript C to denote straight. This is a semi-dominant trait, though, so that means that if dogs inherit one copy of this mutation, they will show some portion of the trait or they’ll have generally a wavy coat, if they inherit one copy of the mutation—whereas if a dog inherits two copies of curl, they will have a much tighter curl, like this dog we see here on the right. This dog here actually technically could be a straight-haired dog. Sometimes dogs that have straight hair will have a little bit of a wave to it, but I would assume this dog here in the middle is actually probably a wavy coat. Some Poodles do occasionally carry straight hair, which makes their hair a little bit more wavy in appearance than the very tight curls that are often associated with Poodles. I included the Afghan Hound here, because this is a great example. Since Afghans grow their hair nice and long, it’s easy to see how straight the hair is in this breed. This is definitely a dog that would have two copies of the straight variant. In order to get a dog with the very tight curls, you would have to breed two dogs together that had at least one copy of the CuC variant, and that would give you about 25% with the very tight curls if that was what was done. 

The next one we have on our list is the Hr Locus. It’s in the FOXI3 gene. It’s also called the hairless locus. This has two alleles. One for hairless, which is dominant. It only takes one copy of that hairless mutation in order to produce the hairless appearance in some breeds. And then the small Hr, which is for coated or powderpuff, as it’s often called. It is recessive, so in order to get a powderpuff dog, you would have to have two copies of the coated version of the gene in order to develop it. You only need a single copy to get the hairlessness. This specific mutation is the mutation which causes the hairlessness that we see in the Chinese Crested, the Peruvian Hairless (which is also called the Peruvian Inca Orchid), and also the Mexican Hairless (or the Xolo). We see this mutation in these breeds. It is not associated with the hairlessness that we see in the American Hairless Terrier, which is actually a different genetic mutation, which is recessive. This is a different mutation. Sometimes, dogs with the hairless mutation still grow hair. This occasionally happens in Chinese Crested, referred to as Hairy Hairless dogs. The reason it’s important to have this testing is because we want to test our haired dogs to see whether they do or don’t have that hairless variant. The reason that’s concerning is because when you breed two hairless dogs together (again, this is a dominant trait; we talked about it in the same way in merle), we could potentially get about 25% of the litter that would have two copies of hairless. Those dogs will actually, just like with other dominant traits, pass away in utero and you’d have a smaller litter size, just like in those Harlequin Danes. Again, the ideal situation (if you wanted to maintain the largest litter size you could) is you would breed a coated dog that does not carry hairless to a hairless dog. That would give you the largest litter you could. It is important to test those coated dogs for the hairless first, to make sure that they don’t carry that hairless variant. That being said, that would end up producing a litter that’s about half hairless and about half powderpuff in that particular case. Very common that that is done in these breeds that have this hairless appearance. 

The next one is an important one that we see in a lot of different breeds. We refer to this location as IC Locus. It’s in the RSPO2 gene. It’s also called the improper coat or furnishings locus. Essentially what furnishings are are this long hair that we develop on the face: mustache and long eyebrows that we see in a variety of different breeds. All three of these dogs here showing different variations on that theme. There are two different alleles here. The F for furnishings, and that is dominant to improper coat. Improper coat—the name can be somewhat confusing to people, because really all improper coat is is short hair on the face. It has nothing to do with the remainder of the coat of the dog. It’s just the dogs with “improper coat” that have short hair on the face. It’s only called improper because breeds that we really want to have these furnishings on, if they don’t have that, then they technically have an improper coat. Improper coat is actually the normal version of coat on the face for a wide variety of breeds, including Labradors, Golden Retrievers—any breed that has the short hair on the face. Improper coat is somewhat of a misnomer in those breeds. Dogs that inherit two copies of the improper coat allele lack the furnishings on the face. As I mentioned, improper coat is normal for some breeds. So dogs which carry one copy of IC or if they actually have IC, in addition to having an improper coat that they may have if they’ve got two copies of this—dogs that carry the improper coat variant are also more likely to shed. They tend to shed a little bit more than dogs that have two copies of furnishings, like these dogs down below here. Interestingly, sometimes people get confused with the improper coat situation and how it may impact the rest of the coat of the dog. This picture here is of some Irish Water Spaniels. Irish Water Spaniels are a great example of a dog that has a long curly coat everywhere else on its body but actually has “improper coat” on the face. That’s why their facial hair is so darn short there on the face. This is occasionally seen in Poodles as well. Poodles do carry improper coat out there and if two poodles happen to be bred together that both carry it, then you may end up with some dogs that look more like this. Obviously, a lot of the show Poodles have all of their facial hair trimmed so they look like this, but sometimes it could be something that’s seen naturally as well in these dogs. 

Another interesting thing about this, too, is that all wirehaired dogs have facial furnishings but not all dogs with facial furnishings have wirehair. So this little Border Terrier here on the left has more of that wiry characteristic to the coat. A lot of the texture of the coat that we see can be changed by the L Locus, which we’ll get to next! Dogs that have long hair (along with facial furnishings) tend to have their hair be a lot softer in general, whereas a lot of these terriers that have their facial furnishings—they tend to have shorter hair and don’t have this long hair variant. Their hair tends to have a lot more wiry texture to it. When it comes to the L Locus, there are two general alleles that we talk about. We talked about short hair and long hair: Sh versus Lh. Short hair is dominant. It does require two copies of long hair to produce the long-haired variant. A dog that carries one (or two) copy of short hair will have short hair. The long hair tends to make the hair softer in dogs that also have those facial furnishings. 

Here we have a situation similar to the D Locus where we actually have multiple genetics variants again in the same gene that coat for long hair. If a dog inherits any one of these variants from both parents, they will have long hair. Each of these variants is found in different breeds, kind of like the way the two variants for coat-color dilution are found in different breeds. Certain breeds carry these particular variants. Right now at Paw Print Genetics, we’re testing for three of the known variants: The Lh1, the Lh2, and the Lh4. Some breeds do carry multiple of these. For example, the French Bulldog (I did get a question about this). French Bulldogs actually carry two of the mutations. They can carry the Lh1 mutation but they also could carry the Lh4. Both of those are important to look at in breeds like the French Bulldog. Afghan Hound is also another that carries both of those. Those are important to look at when you test. We actually have individual tests for all of these variants at Paw Print. They can be tested for. Just like with dogs that have the coat color dilution, dogs that have, say, an Lh1 and an Lh4 (one from each parent), they will still have long hair, even if they don’t have two copies of the exact same mutation. They can still have long hair. This Eurasiaer here in the middle—they have multiple mutations for long hair in them. They may have one other one that’s not notated here. All of these breeds have variations on the long hair that give them their appearance. 

The last thing we’ll talk about today is the SD Locus, or shedding locus. It’s found in the MC5R gene. There are two general alleles that we talk about: the high shedding versus low shedding. This, similar to curl, is a semi-dominant trait. If a dog inherits one copy of high shedding and one copy of low shedding, they’re going to fall out somewhere in the middle on shedding, more of a moderate shedding. The general characteristics are here. If you get two copies of low shedding, that dog would typically be a lower shedding dog. It is all quantitative versus qualitative. There are definitely going to be other variants or other genetic factors that play a role in shedding. One that we know of is the IC Locus, as I mentioned. Because dogs that carry the IC variant are more likely to shed. Dogs that carry two copies of IC are even more likely to shed. We have to look at both the IC Locus and the shedding locus together in order to get an overall general idea of how likely a dog might be to shed. There is one major caveat to all this, though. It seems that the SD test results don’t correlate well with shedding in Poodles or Poodle mixes. We don’t understand this yet, but it probably has something to do with other genetic background and other factors that Poodles or Poodle mixes are carrying. It’s not uncommon for us to actually find Poodles that technically would be high shedding, if we were only looking at the SD Locus. Their test results there would appear high shedding. They may not be more highly shedding than other dogs. At this time, there are some people that have decided not to use this in Poodles or Poodle mixes because they just haven’t seen a great correlation with it in their particular line. That may be something to consider. There are other factors that probably play an important role in shedding that we don’t yet know, but we know that this SD Locus along with the IC Locus does have some pretty significant control over that in dogs. 

I guess we do have one more. That’s the T Locus trait. That is responsible for a natural bobtail that we see in a host of different breeds. There are two alleles to this as well. The bobtail is actually dominant, so it only requires one copy of bobtail to give them this bobtail appearance, like we see in these two breeds here: the Australian Stumpy Tail Cattle Dog and the Brittany, both of which carry this particular genetic mutation at times. In some breeds, not every dog will have a natural bobtail by any means. In fact, natural bobtails are these dominant mutations which are a little bit concerning because (just like with the harlequin and some of the other variants that we talked about that are dominant) if dogs inherit two copies of bobtail, they also die in utero. You would have a smaller litter size of about 25% if you breed two bobtail dogs together. It is very helpful to test for bobtail, though, because there is a wide variability of bobtail in dogs. There can be some dogs that technically have the bobtail mutation where their tail almost looks normal. You would not know. But if you happen to breed that dog to another bobtail, you could end up with a smaller litter size. Sometimes testing dogs that have a somewhat normal-looking tail to see if they happen to carry that bobtail could be beneficial. You probably wouldn’t need to test your dog if it came out with an obviously bobtail because it would likely be due to this. This particular mutation is found in a lot of different breeds. There are some other breeds that it’s not found in that do have bobtail. For instance, the bobtail that we see in Bulldogs, Boston Terriers, Rottweilers—the cause of the bobtail in those dogs is actually not known. There’s a different genetic factor that at this time, we don’t know. But this is a very common cause of the bobtail we see in the Australian Cattle Dog, the Australian Shepherd, the Brittany. If we were to breed these dogs, we would want to try to avoid two dogs with the bobtail mutation together in order to prevent litters from being smaller.

That gets through all of the things I had to present today. I do have a couple of questions I got ahead of time that don’t quite fit in to what I was previously talking about. There was a question about brindle that we previously talked about. Somebody had asked: Is coat color breed-specific, genetically? It’s not fully breed-specific, because a lot of these mutations are shared across multiple breeds, across the canine world. But sometimes some of the nuances of the particular colors could be more breed-specific because of the genetic background of the breed or the individual. There can be some nuances in the way that these colors actually appear in the dogs. Someone asked how they would determine if a Dachshund carried piebald or dapple genetics. Dapple is just another term for merle. In order to test a Dachshund to see if they carry piebald, it would be the S Locus, which is similar for all Dachshunds. And then the dapple would be the M Locus or merle. There were a couple of questions about the actual thickness of coat or the coarseness in dogs. There really isn’t a lot of genetic testing in order to be able to test either the thickness or the texture of the coat at this time. The one thing that we do know the texture of the coat for is in long-haired dogs that also have the facial furnishings—they tend to have a little bit softer coat. Other than that, we don’t have a lot of genetics available to help us with coat quality. 

Laura Reeves [1:10:13] Judi, do you have some more stuff for us? 

Dr. Judi Stella [1:10:35] We have a couple questions about Portugese Water Dogs. The Cu—is that the same curly gene in Portugese Water Dogs? 

Dr. Casey Carl [1:10:25] Yes, I believe it is in Portuguese Water Dogs. There is another cause of curl as well that we’re not currently tested for. I believe it’s found originally in the curly-coated Retriever, but it’s also found in some other breeds as well. As far as I’m aware (and I may have to go back and verify this), I do believe that in Portuguese Water Dogs it is the Cu that we test for that’s the one typically seen in theme. 

Dr. Judi Stella [1:10:50] They can have improper coat, but it makes them look like a Lab and they shed. Is that the IC Locus? Or the L Locus?

Dr. Casey Carl [1:11:00] Yes, so the L Locus in most of these breeds would be expected to be two copies of long hair, in most of those breeds like the Poodle or the Portuguese Water Dog that have the hair that continues to grow. In terms of the IC Locus, I would guess it would be the IC Locus that is causing that, based upon what they’ve described. We do see it in the Poodle on occasion, so it wouldn’t surprise me if that was also present in other breeds. If a dog comes out looking like a Lab, I think it’s fair to say that in most cases, it probably is the IC Locus that’s responsible for that. 

Dr. Judi Stella [1:11:46] Why do Afghan Hounds have facial hair when they’re pups?

Dr. Casey Carl [1:11:51] That’s a good question. I don’t know!

Laura Reeves [1:11:57] Fluffy things on their faces that fall off when they get older. 

Dr. Casey Carl [1:12:02] That’s a good question. I don’t know that anyone knows that. Maybe somebody has looked into that, but I am not familiar. 

Laura Reeves [1:12:09] Then they have these long goatees. It’s amazing. 

Dr. Casey Carl [1:12:15] I don’t know. I’m not sure why that would be. 

Dr. Judi Stella [1:12:25] What would cause a dog to be born without a tail that is not in a breed normally having bobtails and there’s no history of bobtails from any generations?

Dr. Casey Carl [1:12:34] There could be a lot of different causes. There are other causes of bobtail out there. In some cases, it may not actually be inherited. There can be some developmental issues that can happen in dogs, where maybe they could be born with a smaller tail. I don’t know that we have all of those things understood. The natural bobtail that we test for is just one of multiples. Something just came to mind: It’s something new that we started doing at Paw Print. It goes back to the IC Locus. There is another genetic variant that we actually found at the IC Locus. I didn’t have a chance to update all of these slides to discuss it, but there is another mutation which occurs in some dogs that result in something that we refer to as weak furnishings. It’s only seen in dogs if they inherit two copies of this weak furnishings variant from each parent. We’re actually testing for this now at Paw Print. We’ve recently updated things. What we found is if dogs have these weak furnishings, they technically have furnishings, but they aren’t very visible when they’re first born and they slowly fill in over the first six months or so of their life. A dog that has either two copies of weak furnishings or if they have one copy of weak furnishings and one copy of improper coat, they often will have this appearance where it doesn’t fully fill in these furnishings until they get quite a bit older. That is something that we can now also detect. Anybody that’s out there that breeds varieties of dogs that have furnishings, they might have seen this in some dogs that seem to be slow to develop this. We have found the specific genetic mutation that is causing that in these dogs. That can be seen now. Something that can be really helpful in some cases. 

Laura Reeves [1:14:23] Judi, did you see this one about the Podengos at the bottom? I thought that was interesting. How is distichiasis passed or inherited in Portuguese Podengo?

Dr. Casey Carl [1:13:11] I think that it potentially can be inherited. I don’t know that it is in all cases. There’s no genetic testing available for distichiasis. Unfortunately, I don’t have a great answer for that. That’s essentially a double row of eyelashes or eyelash abnormalities. 

Dr. Judi Stella [1:15:19] Do Borzoi have wavy genes?

Dr. Casey Carl [1:15:23] I don’t know if they do or not. They do have a pretty straight looking coat. Sometimes these very straight looking coats can have some wave in them. I would be surprised if they did, because that would mean that occasionally we may end up seeing some curly coated Borzois. If we do so see some very curly coated ones, we might. But I’m not certain. We don’t test a lot of Borzois for that, so I’m not sure how widespread that might be in the breed. 

Laura Reeves [1:15:55] I would say they have curly and straight. Judi, what about this one about the genes responsible for blue merle in Collies? Dr. Carl, Ramona asks: She’s seen or read something that there are at least six genes responsible for blue merle in Collies that cause different colors: light blue, pewter, double merle, all that. 

Dr. Casey Carl [1:16:30] There’s really only this one mutation: the merle mutation, which is responsible for that. They might be referring to the different groups that these dogs are placed in based upon the size of their merle mutation. There are other schemes out there that do have more than just the four groups that we use at Paw Print Genetics. She may be referring to some of these other schemes. It really is just that one M Locus mutation that’s responsible. It’s just the different size of that merle mutation that’s responsible for all those variations. 

Dr. Judi Stella [1:17:01] We do have another one about the hairless, specifically in the Chinese Crested: Do you know why different hairless dogs would produce different degrees of hairlessness? 

Dr. Casey Carl [1:17:14] It’s probably more to do with some of the genetic background. We don’t fully know why that works that way. Technically, these dogs have a condition known as epidermal dysplasia, which ends up resulting in their appearance, which is why they have slightly abnormal teeth as well that go with that. In terms of the more specific reasons why one dog might have hair and one dog wouldn’t,  we don’t know yet. 

Dr. Judi Stella [1:17:42] Can you review again the lethal in-utero mortality? What of the coloring coat genes cause that? 

Dr. Casey Carl [1:17:51] Yes. It’s going to be those dominant ones, the ones that we talked about specifically would be the H Locus for the harlequin in the Great Dane, the M Locus for merle would be a concern, the T Locus for the natural bobtail, and there was one other one that we talked about. The hairlessness (Hr). All of those potentially run into that situation where if you have dogs carrying two copies of that dominant mutation, that could give you some issues. 

Dr. Judi Stella [1:18:47] Are any coat colors controlled by epigenetic mechanisms? 

Dr. Casey Carl [1:18:50] Yeah! Probably all of them. That is probably a major factor in all of that. At this time, though we don’t fully understand all of that. When it comes to the diseases we test for and things like that, a lot of the things we’re doing are the lowest-hanging fruit in the sense that these are the ones with a direct one-to-one correlation between the mutation and the actual trait or disease that we see. In actuality, a lot of traits and a lot of diseases are much more gray in the sense that there’s a lot more variables that play a role in dictating that. I think as we move forward in genetics and dogs, we’re going to see this be the case where we’re going to find that certain characteristics or diseases actually have a lot more gray area. There’s probably multiple genes involved, whereas a single mutation is more the exception than the rule. 

Dr. Judi Stella [1:19:40] We had a question about urajiro inheritance too? With Shibas? 

Dr. Casey Carl [1:19:47] We don’t know that yet. That’s the very light underbody color that we see in Shibas. There are some other breeds that also have it. Unfortunately, we don’t know the genetics behind that yet. 

Dr. Judi Stella [1:20:27] There are a couple of questions about what causes a kink in a tail. 

Dr. Casey Carl [1:20:29] It can be the bobtail locus. It can occur. But there are other reasons, too. Sometimes it can just be an in-utero issue. Maybe the tail was kinked in utero. There can be a lot of different reasons. We don’t have a genetic understanding for it or testing available for it at this time. In some cases, it could potentially be inherited but there’s also some non-inherited reasons for the kink tail as well. 

Dr. Judi Stella [1:20:45] I think we got most of these. For any of them that we didn’t or that are a little bit outside of the topic of discussion here, we’ll take those into consideration and see if we can ask Dr. Casey Carl to join us again. I know CDDY IVDD is really something I would like to have a lecture on if that would be possible. Maybe after the new year, we can see if you have some time to join us again, because this was great. Everybody is sending in thank yous. 

Laura Reeves [1:21:19] I see some potential for Dr. Carl to join us on the future interactive podcast series. 

Dr. Casey Carl [1:21:32] There’s all sorts of things possible! Lots of things we could talk about. I posted my contact information here for you guys as well. You’re more than welcome to reach me at Paw Print Genetics. Also, you can reach out and send a friend request to me on Facebook. I won’t send you anything annoying. On occasion, I’ll send on information about sales at Paw Print and things like that, but that would be the vast majority of it, and I won’t sell your information to anybody else. More than anything, it’s just a way for me to contact people via social media. You’re also very welcome to just send me an email there or give us a call during the weekday, and I’d be more than happy to chat with you and answer any questions you have. This is something we take very, very seriously at Paw Print: talking with our clients and trying to assist people in using the genetic test results that they get back. Unfortunately, historically, laboratories haven’t been very good at that. It’s something that’s very crucial for all of the dog breeders out there to have that resource. We’re very happy to be that resource for everyone. 

Cat Matloub [1:22:36] I think I speak for every single person and breeder in our community when I say we can’t get enough of all the expertise you have, and we have so many questions and can’t wait for the next time that we can grab some of your time. For everybody out there, we’ll be making an exciting announcement about a special offer for the month of December with Good Dog in partnership with Paw Print. Keep an eye out for that. We’ll be doing lots more good stuff together. Thank you, thank you, thank you all for your questions and for being so engaged. And thank you, Dr. Carl. Thank you, Laura. 

Dr. Casey Carl [1:22:51] Thank you guys so much for having me. I want to give a shoutout to Good Dog as well, because I think what Good Dog is doing is absolutely amazing for the dog breeding community. I think you guys are on the right path, and I’m really excited to be a part of what you guys are doing and to be able to offer this information to all of your members; it’s really awesome. Keep up the good work, you guys. I know we’ll do some more things together in the future. I really look forward to it.