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, we’ll 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
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
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 dog’s
ears are colored, it can hear, white ears, it’s 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
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