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BASIC GENETICS IN GREAT DANES

 

 

 

 

Take a look at your dog. You can see quite a few things about her. You can tell what her coat color is, if her hair is long or short, what her eye color is. You can even "look" through the use of x-rays and laboratory tests, to determine if her hips are sound, and if her thyroid gland it working properly. All of these things make up the dog's phenotype.

 

Your dog's genotype refers to what is actually present in her DNA, whether or not that has transferred to her appearance, build, how her body functions. Each dog has two full sets of genetic information, one from each parent. So each locus (genetic unit) has a pair of genes. This pair of genes can be either homozygous meaning that both of the genes in the pair are identical or heterozygous meaning that the two genes are different. There may only be two options for a particular locus, or there may be many options. Any single trait may be controlled by a single locus, a single pair of genes, or it may be controlled by the combination and interaction of many pairs of genes. The available genetic options at each locus are called alleles.

 

Dominant and recessive refer to the gene's behavior if they are different. In simple terms, if the two genes at a locus are different, the dominant gene will determine the dog's phenotype, what you see. A dog will only show a recessive trait if BOTH genes at a locus are the recessive allele. Both dominants or one dominant and one recessive will result in the dominant phenotype. Dominant and recessive DO NOT mean "good" and "bad." In fact, many desirable traits in Great Danes are the result of recessive genes. However, it is easier to "breed away" from a bad dominant gene--if the gene is there, you see it, and you can choose not to breed the animal displaying the trait. A recessive trait can be carried, hidden, for many generations, and will never display the trait unless it gets paired up with another matching recessive gene from the other side of the family.

 

Unfortunately, not everything works as a simple dominant/recessive. At some loci, the different alleles may have a relationship of incomplete dominance. That is, if both genes are recessive, the trait coded by the recessive will be displayed. If the locus is heterozygous, the phenotype will show a "halfway in between" appearance. Only when the locus is homozygous for the dominant will the appearance show the dominant gene.

 

In a simple case, there are only two alleles that can appear there. That locus will either be homozygous for the dominant, heterozygous, or homozygous for the recessive. Homozygous dominant, the dominant trait will appear. Likewise if it is homozygous recessive, the recessive trait will appear. In the heterozygous case, you will see either the dominant phenotype (if the alleles have simple dominant-recessive relationship) or a phenotype that is halfway in between (if there is an incomplete dominance relationship.) At some gene loci, there are several genes that can appear there. Many times, we can rank these allelles in order of dominance. Since only two allelles will be present in any one dog, we can still use the dominant-recessive idea to see what will or could be produced.

 

Primary Coat Color

 

First, well look at the different loci that affect coat color in the Great Dane.

 

In each series, the possible alleles will be listed in terms of dominance, with the more dominant genes at the top, ranging to the most recessive at the bottom. The usual convention is to have the dominant gene capitalized, with recessive genes in lower case letters.

 

To begin, we'll touch on three series, the A-series, the E-series and the D-series. While all three do affect coat color in Great Danes, my intention here is to discuss primarily the Black, Harlequin, Mantle, Merle and White colors. All of these colors are AA, EE, and DD.

 

A-series: This determines the "base" color of the coat. Dogs have two forms of melanin in their coats. One, eumelanin, is dark. It varies in color due to variations in the protein that forms the framework of the pigment granule. The base form of eumelanin is black. Eumelanin can also be brown (also called chocolate or liver) or blue-grey. The other pigment, phaeomelanin, ranges from pale cream through shades of yellow, tan and red to mahogany.

 

The available alleles are:

 

A Dominant Black eumelanin can appear everywhere. A is seen in Black, Blue, Merle, Harlequin, and White Great Danes.

 

ag Agouti or wolf gray (not present in Great Danes) Each hair is banded with eumelanin and phaeomelanin.

 

ay Sable Each hair is the phaeomelanin color with eumelanin only at the tip. The ay genotype (always homozygous in Great Danes, acts, IN DANES as a simple recessive to A) is responsible for the base color in Fawn and Brindle Danes. Modifiers can increase or reduce the amount of black tipping. In Great Danes, we have selected for modifiers to reduce this tipping, although it is still often visible at the base of the tail and around the ears.

 

at Tanpoint, Doberman and Rottweiller color (not present in Great Danes) Eumelanin color with only phaeomelanin at the "points" on the face, legs, under the tail.

 

as Saddle more tan than tanpoint, seen in German Shepherd Dogs (not present in Great Danes) As tanpoint above, but with far larger areas of phaeomelanin only.

 

a Recessive black (not present in Great Danes)

 

E-series: The E-series is poorly understood and very controversial. In the simplest form, E=can produce eumelanin, and e=only phaeomelanin is produced (regardless of the A-series genes, and ee dog will show ONLY the yellow/red pigment, as is seen in yellow Labradors and Irish Setters.)

 

There are some theories that Masking (as on our Fawns) and Brindling are also on the E-series. Other research indicates that one or both of these traits are at a different locus altogether. In any case, all Great Danes can produce black pigment.

 

For now, I'm assuming (only further research will allow us to know for sure) that Brindling is on separate locus, that I'll call Br=Brindle, br=not-brindle. What is clear is that Brindle is dominant to Not-Brindle.

 

D-series: This determines whether the recessive gene that makes the eumelanin Blue instead of Black is present. There are only two alleles.

 

D Normal (Black) pigment

 

d Blue dilution. All areas that the A-series codes as Black will be Blue in color. Note that dd can affect the mask and/or stripes in Fawns and Brindles.

 

Other loci that affect coat color in dogs, but do not enter into discussion of the Great Dane are:

 

C albino series. All Great Danes are C, no albino traits. Other more recessive alleles range from slight to full fading of color.

 

G graying The dominant G causes puppies that are born dark, with the color fading as they mature. All Great Danes are gg, no graying.

 

T ticking series. The dominant T produces individual pigmented hairs through spots of colored hair in otherwise white areas on the dog. All Great Danes are tt, no ticking.

 

B brown The recessive causes the eumelanin to be red/brown in color. The recessive b should not be present in Great Danes, although there is some chance that it is. The homozygous recessive bb produces red Dobermans and chocolate Labradors. If present, it could produce chocolate Danes, "red merle" Danes, or a brown mask and/or stripes on Fawns and Brindles.

 

So, the Black, Harlequin, Merle, Mantle, and White Great Danes are ALL AAEEDDCCggttBB. To simplify discussion, we will ignore these genes in the rest of our discussion, as all loci are homozygous for a particular gene, these alleles will not vary from individual to individual.

 

Pattern

 

From the series previously discussed, we now are left with solid Black dogs. Three gene series are responsible for creating the wide range of colors/patterns seen in the Harlequin color-group of Great Danes.

 

M-Series: merle. This gene is an incomplete dominant. There are two alleles:

 

M merle

m not-merle

 

There are thus three possible combinations of the above in any one dog:

 

mm Black

 

Mm Merle, the coat color is diluted to a blue/grey shade with irregular patches of black

MM "double-merle" The diluting action of the merle gene dilutes almost all of the pigment to white.

Double-merle white Danes may have a few patches of merle and/or black, usually on the head or at the base of the tail, but the dog will be predominantly white.

 

H-series: Harlequin gene. This too is an incomplete dominant, but with some additional complications. The two alleles are:

 

H Harlequin

h not-harlequin

 

The dominant gene H ONLY has an effect of the phenotype in combination with the Merle gene. If a dog is mm (not-merle) the H gene may very well be present, but will have NO effect on the dog's appearance. As with Merle, there are three possible combinations of these genes, but only two appear in dogs.

 

hh not-Harlequin

 

Hh IF the dog also carries M, then the partially diluted blue/gray areas become fully diluted to white. The irregular black patches are unaffected.

 

HH This combination is a prenatal lethal. Any fertilized egg that has the HH genotype does not develop into a puppy.

 

Looking only at the above two genes, we have the following possible combinations:

 

mmhh Black (not carrying Harle)

mmHh Black (carrying Harle)

Mmhh Merle

MmHh Harlequin

MMhh White (not carrying Harle)

MMHh White (carrying Harle)

 

S-Series: White Spotting. There are several alleles at this locus. Although ranked by dominance, all show a pattern of incomplete dominance, with the resulting pattern being in between the two alleles in a heterozygous dog. The pattern seems to lean a bit more in the direction of the dominant of the two alleles, but still is in between the patterns coded by each of the two genes that is present in the individual dog. There are also plus and minus modifiers that affect somewhat the amount of white, meaning that each genetic combination will show variation. Between the effect of each gene being varied by the plus and minus modifiers, and the incomplete dominance action of these alleles, guessing S-series patterning from looking at a dog (rather than also examining the parents and offspring) can be difficult.

 

S solid. An SS dog may still show very minimal white at the chest and feet. Generally with this gene pair SS, the white will cover less than 5% of the total body area.

 

si Irish Spotting. White appears on the chest, feet, face, neck, and tail tip. The sisi combination will result in a dog that is about 25% white. These dogs might or might not show the full collar.

 

sp Piebald. An spsp dog is about 50% white, resulting in a parti-color dog, as is seen in Cocker Spaniels and Brittanies. Might not be present in Great Danes.

 

sw extreme white spotting. The Irish spotting pattern extends even farther, covering almost all of the dog except the head and possibly a saddle or large rounded patch(es) on the back. This pattern is sometimes called Piebald in Great Danes, but is not the result of the sp piebald gene. In some herding breeds, where the genetics of this pattern have been more closely examined, this pattern is often referred to as "color-headed white."

 

Now let's look at the appearance of some of the heterozygous possibilities.

 

Ssi Showing up in Harlequin-breeding litters, these dogs are often referred to as "pet-marked blacks." They show too much white to be shown as Blacks, but not enough white to be considered Mantle

 

Ssw These dogs will look almost exactly the same as an sisi Irish marked dog. All "flashy" boxers (which look like "Mantle Boxers" in Great Dane terminology) are actually Ssw, NOT sisi.

 

sisw These dogs are usually Mantles with quite a bit of white. The full collar, and often the white on the chest extending all the way down the front legs, and a full white belly. Will probably appear more like a White Dane with a Boston head and a large blanket of black on the back.

 

Although the white patterns are easily visible on Black and Merle Danes, there are obvious complications in determining the white pattern on a Harlequin, due the impossibility of distinguishing white caused by the H-series from white caused by the S-series.

 

The Mantle

 

In her "The Case For Approving the Mantle: As Simple As Black and White" (http://www.users.cts.com/king/g/gdca/issues.html) Mary Anne Zenetos presents some excellent arguments in favor of accepting the Mantle in the conformation ring from the point of view of breeding for the Harlequin pattern. Specifically, she cites the use of Mantles in Harlequin breeding to provide the clean white fronts and necks that are desirable. She observes that Harlequin pedigrees do not accurately represent the quality of breeding, because the Mantles cannot be shown, therefore quality Mantles cannot achieve an AKC championship. This, if one is merely looking at the number of finished ancestors, makes most Harlequins appear to be of lesser quality than the other accepted colors where all ancestors will have been of showable colors also. And she is correct.

 

However. She states that Mantle x Mantle will always produce Mantle. Ms. Zanetos seems to believe that all Mantles are, in fact, sisi. If that were the case, she would be again correct. Now, in several of the herding breeds, there is ALWAYS the white pattern. The "normal" white pattern generally includes the paws, tail tip, chest, and the front of the neck. Those dogs with a full white collar are referred to as "white-factored." From the breeding records of these herding breeds, we can clearly see that the "normal white pattern" dogs are sisi. And the "white-factored" dogs are sisw. This is evidenced by the fact that white-factored X white-factored produces, on the average, 25% normal white, 50% white-factored, and 25% color-headed white (showable in collies, but not in Aussies or Shelties.)

 

Our current Mantle standard states that "The color shall be black and white with a solid black blanket extending over the body; black skull with white muzzle; white blaze is optional; whole white collar preferred; a white chest; white on part or whole of forelegs and hind legs; white tipped black tail. A small white marking in the black blanket is acceptable, as is a break in the white collar." See http://www.gdr.com/deptment/mantle.htm

 

Now, bearing in mind that the phenotypes of various s-series genotypes tend toward a lot of overlap (i.e. an sisi dog *could* have a full collar, but it's unlikely, and an sisw dog *might* be lacking the full collar, but again, it's unlikely) what we are declaring the "ideal" Mantle is most likely to be the sisw genotype. This means that two "perfectly marked Mantles", when bred to each other, are going to produce 25% "too little white" Mantles, 50% "perfectly marked" Mantles, and 25% color-headed whites.

 

The existance of color-headed white Danes (often mistakenly called "piebald" in Danes, although the sp piebald gene is probably *not* present in Great Danes) is proof enough that the sw allele IS indeed present in our gene pool.

 

I would also like to touch upon the example of the Boxer. Boxers come in (in Boxer terminology) "plain" and "flashy." Basically, "plain" means "solid." And "flashy" means the same as our "Mantle." *In Boxers,* we know that the Mantle/flashy pattern is not sisi, the si allele is not present in the Boxer gene pool. All flashy Boxers are, in fact, Ssw. Meaning that flashyXflashy results in 25% plain, 50% flashy, and 25% color headed whites. Many, although not all, "white" boxers are deaf.

 

As, up until now, there was no reason to breed Mantle X Mantle, those color headed whites turning up in Harlequin litters were assumed to be either oddly marked Harlequins, or else assumed to be double-merle whites. In fact, many of them were swsw whites. By making the breeding goal for the Mantle include the full white collar, we are, in effect, requiring that we maintain the sw allele in our gene pool, thus actually increasing the number of deaf almost-white puppies born.

 

White and Deafness

 

There is a definite connection between White and Deafness in Great Danes. The melanocytes, the cells that produce the eumelenain and phaeomelanin pigment in dogs are derived from the neural crest cells.

 

Early in embryonic development, a group of cells differentiate to form the neural crest cells. The majority of these cells for the brain and nervous system. A few "leftover" neural crest cells go on to form the melanocytes. These cells start of in specific pairs of areas on the head and along the back, and migrate down over the dog as it develops. It is, perhaps, easiest to imagine this in terms of paired areas where paint is poured, running down over the head and back. With the S-series, the SS dogs have paint that gets (almost) everywhere. From the starting points, the furthest reaches are, of course, the chest and toes, where these SS dogs may have some white.

 

The si allele limits the amount of paint, leaving much more white at the feet, belly, chest, tail tip, and the white facial markings.

 

The sp allele tends to produce less symmetrical effects than si or sw, perhaps acting by turning off half of one or more pairs of sites.

 

And the sw allele allows almost no paint, leaving color only on the head and possibly a round patch or two on the back or rump.

 

The M gene seems to act more by affecting the survival of these neural crest cells. The migration pattern of these cells is still determined by the S-series, but in the gray (or in Harlequins, white) areas have limited melanocytes. Most of the dog has no melanocytes in the MM double merle Whites.

 

The inner ear has small hairs in it. If these hairs are unpigmented, the dog is deaf. It is unclear whether pigment itself is the issue, or whether lack of pigmentation merely indicates that no neural crest cells are present. In any event, the lack of pigmentation of these hairs is linked to deafness, regardless of the actual cause and effect relationship. Both the MM gentotype and the swsw genotype can and do produce deafness.

 

So, the lack of pigment in White Danes is indeed linked to deafness. The old "rule" that if a dogs ears are colored, it can hear, white ears, its deaf, while not a hard and fast rule, does have some merit. Color on the ears certainly indicates that surviving neural crest cells are present in the ear area, making it more likely that the dog can hear.

 

Breeding-Where do Deaf Whites Come From?

 

We've now covered the genetics that make up Black, Harlequin, Merle and (double merle) White. Let's take a look at what we get when we start breeding these dogs. For now, let's disregard S-series white spotting. We'll take a look at it again later. For Black and White Danes, I'll use BlackH and WhiteH if these dogs are carrying the H gene. Please note that these percentages are theoretical, given that HH is lethal.

 

However, MMHh is also a sub-lethal, in that some MMHh dogs also do not develop, so the WhiteH numbers stated are HIGHER than would actually be expected in actual puppies born. While it may be possible to distinguish WhiteH from White because the WhiteH, while rarer, should show only black patches on the few areas of pigment, whereas a White (not carrying Harle) can show Merle and Black patches. There is no way to visually distinguish between Black and BlackH.

 

!=will produce double-merle white puppies, *=will produce Harlequin

 

Breeding

Genotypes

Offspring

Black x Black

mmhh x mmhh

100% Black

Black x BlackH

mmhh x mmHh

50% Black, 50% BlackH

Black x Merle

mmhh x Mmhh

50% Black, 50% Merle

Black x Harlequin

mmhh x MmHh

25% Harle, 25% Merle, 25% Black, 25% BlackH

Black x White

mmhh x MMhh

100% Merle

*

Black x WhiteH

mmhh x MMHh

50% Merle, 50% Harle

BlackH x BlackH

mmhh x mmHh

50% Black x 50% BlackH

*

BlackH x Merle

mmHh x Mmhh

25% Black, 25% BlackH, 25% Merle, 25% Harle

*

BlackH x Harlequin

mmHh x MmHh

33%BlackH, 16.7%Black, 33%Harle, 16.7% Merle

*

BlackH x White

mmHh x MMhh

50% Merle, 50% Harle

*

BlackH x WhiteH

mmHh x MMHh

33% Merle, 67% Harle

!

Merle x Merle

Mmhh x Mmhh

25% Black, 50% Merle, 25% White

!*

Merle x Harlequin

Mmhh x MmHh

25% Merle, 25% Harle, 12.5% Black, 12.5% BlackH, 12.5% White, 12.5% WhiteH

!

Merle x White

Mmhh x MMhh

50% Merle, 50% White

!*

Merle x WhiteH

Mmhh x MMHh

25% Merle, 25% Harle, 25% White, 25% WhiteH

!*

Harlequin x Harlequin

MmHh x MmHh

8.3% Black, 16.7% BlackH, 33.3% Harle, 16.7% Merle, 16.7% WhiteH, 8.3% White

!*

Harlequin x White

MmHh x MMhh

25% Merle, 25% Harle, 25% White, 25% WhiteH

!*

Harlequin x WhiteH

MmHh x MMHh

33.3% WhiteH, 16.7% White, 33.3% Harle, 16.7% Merle

!

White x White

MMhh x MMhh

100% White

!

White x WhiteH

MMhh x MMHh

50% White, 50% WhiteH

!

WhiteH x WhiteH

MMHh x MMHh

66.7% WhiteH, 33.3% White

 

The GDCA Color Code

 

Let's take a look at the GDCA color code. The full text is available at http://www.users.cts.com/king/g/gdca/colrcode.html

 

The color code specifically prohibits certain crosses.

 

A Blue cannot be bred to a Fawn or Brindle. This eliminates tainting the Fawn/Brindle gene pool with the d blue-dilution allele. By eliminating this allele from that gene pool, we eliminate the risk of ending up with Fawn with blue masks, and of Brindles with blue masks and stripes. As a blue-masked Fawn or blue striped Brindle is not showable, this prohibition makes sense from an AESTHETIC standpoint.

 

A Blue cannot be bred to a Harle, or Black-from-Harle. Again, we eliminate tainting the Harlequin gene pool with the recessive d blue-dilution allele. This eliminates any risk of producing "Harlequins" with blue torn patches instead of black. Again, and aesthetic decision.

 

A Fawn or Brindle cannot be bred into a Harlequin line. This eliminates having the recessive ay allele in Harlequin bloodlines. And eliminates the risk of "Fawnequins" or "Brindlequins." Again, aesthetics.

 

Not mixing Harle and Fawn/Brindle does accomplish one thing. It eliminates what are called "sable merles" in the herding breeds. These dogs appear sable (the same genotype as our Fawn) except the black tipping on the individual hairs shows an overall merled pattern. This pattern is easy to see in the puppy coat, although it is very difficult to see in the adult. Given that in Great Danes we have selected for modifiers to greatly reduce the black tippings on dogs with the ayay genotype, a "Fawn Merle" would be difficult to spot even with the puppy coat, and virtually impossible to recognize in the adult. This could lead to an unknowing and inadvertent Merle x Merle breeding, resulting in whites which may well be deaf. At last! Part of the GDCA color code that actually serves a valid health-related reason!

 

However, the GDCA color code SPECIFICALLY PERMITS:

 

Harle X Harle (resulting in 25% MM whites, many of whom are deaf)

Mantle X Mantle (potentially resulting in 25% swsw color-headed whites, some of whom are deaf)

Mantle x Harle (potentially resulting in 25% swsw color-headed whites, some of whom are deaf.)

 

Does it not strike anyone be me as being very, very odd that our parent club would go to the effort of having a Color Code, but then have the vast majority of the reasons behind the code be purely aesthetic? And still SPECIFICALLY PERMIT those breedings that will inevitably produce puppies with sensory defects?

 

The Great Dane Club of Germany (DDC) specifically prohibited breeding Harlequin X Harlequin in the fall of 1995. This at least prevents (registered) litters that will result in the MM double merle genotype and its associated problems. In most herding breeding that have the M gene, is considered unacceptable to breed merle to sable (our fawn) for the reasons stated above-it's hard to recognize a sable-merle as carrying the M gene. And it's never acceptable to breed MerleXMerle.

 

So why does the GDCA color code ALLOW HarleXHarle (which is genetically MerleXMerle)? I don't know. But perhaps a closer look at the number of deaf white Danes coming through our country's Dane Rescue groups should cause them to reconsider this aspect of the color code, especially in light of the recent acceptance of the Mantle, widening the range of Champion dogs available to the Harlequin gene pool.

 

 

 

Copyright 2001 Dainoak Great Danes. kris@Dainoak.co.uk All rights reserved. However, you are encouraged to copy and distribute this article for non-commercial use with the following restrictions: You may not modify the article in any way. You must include the entire article including the copyright notice. You may not charge any fee for use, copying, nor distribution of the product with the following exceptions: Non-profit organizations may charge a nominal fee (not to exceed $5.00) until and unless notified by the author this is not the case.

 

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