ABOUT WHITE AND
MERLE FRENCH BULLDOG BREEDING
There are two different
genes giving white coat in French Bulldogs:
- first the alleles on the S-locus for varying extension of white
s [i], s [p] and s [w]
- then the merle gene on the M-locus, in double presence MM
giving predominantly white dogs.
This merle mutation in the SILV gene was detected with a DNA test
by GenMARK - but results have been unreliable and the testing has been
Both S- and M-alleles are known to cause among other defects impaired
hearing or deafness. The mutation is found in PMEL17 - a protein
produced by SILV and playing a central part in the pigment cell and also
affected by the MITF. (Prof. K. Murphy et al. - Prof. L. Andersson et
Both the dilute-allele [d] and the merle factor [M] in French
Bulldog breeding are now described in German literature:
Dr. F. Krautwurst, Praktische Genetik für Hundezüchter. Kynos Verlag,
Mürlenbach, 2002, pages 84-85. www.kynos-verlag.de
- quote translated: "For the sake of completeness is also referred to
the fifth colour variety in this breed. It is the ones by the incomplete
dominant Merle-factor produced black/white spotted. As a result of
partial depigmentation of the black basic colour in these dogs arises in
the classical case a change in genotype from mm to Mm."
Breeding for these defect
mutations is of course a serious violation of the coat colour
disqualification stipulations in the official breed standards.
biogenetic research has shown that white coat
colour is caused by mutations in a gene on the S-locus in the
chromosone coding for a certain transcription factor (MITF). This
controls the activity of several other genes and is responsible for the
normal developement of pigmentation, and also other functions like the
hearing. This now explains why some white dogs sometimes are deaf.
Mutations in the same gene also causes a malformation of the eye, an
abnormally small eye - see picture below. The allelic series at the
white spotting (S) locus encodes this microphthalmia-associated
transcription factor (MITF). The three alleles described at this locus
(Irish spotting s(i), piebald s(p) and extreme white s(w) do not
represent three independent mutations but rather different combinations
of a set of regulatory mutations affecting MITF expression. (Prof.
Andersson et al.)
The term merle is used in
genetic literature 1935, quote: "Merle is inherited in an autosomal,
incompletely dominant fashion" (Mitchell, A.L. (1935) J. Hered. 26,
425-430). Further: "Although rare, a dog carrying the merle allele (Mm)
can appear to be nonmerle, which is know as "cryptic" merle, and produce
merle offspring. Dogs homozygous for merle (MM) are known as double
merles and are predominantly white."
According to the geneticist and dog show judge
Clarence Cook Little, The Inheritance of Coat Color in
Dogs, 1957 which is the fundamental work in this field, there are no
alleles on the M-locus in French Bulldogs. But now the Merle pattern has
been presumed to be a very old mutation, present in the genome of the
common ancestor to all dog breeds.
The "jumping" Merle gene is
retrotransposon, which fades the normal hair colour at random
on uneven patches into a lighter shade, co-existing with the
primary coat colour - in this case black was faded into a greyish
Also other primary coat
colours are faded on irregular patches by the Merle gene, into for
example red merle in Dachshounds, Aussies and other breeds. Merle
is not an allowed colour pattern in the FCI Breed Standard for French
Bulldogs. Grey/blue is mentioned to be a
highly undesirable colour by the American breed club - for
- The Merle gene is
autosomal, incompletely dominant. Where the Merle gene has a
double influence on the hair pigment the colour becomes white,
i.e. totally without any pigment. Homozygous MM is predominanty
white and called double white merle in dogs. Such French
Bulldogs presumably also exist. Double white merle individuals often
- but not always - have serious defects in eyes and ears, hearts, nerves
and may have low fertility and viability.
The Merle gene is
concealed by white and by yellow and other light coat colours:
hidden merle-carriers are called cryptic merles M[c].The
difference between the Merle and the cryptic gene is the length of
the deletion in the merle band. Since this band length can change
when the gene is passed on to a puppy, it is possible for it to
change from merle to cryptic OR from cryptic to merle between
a parent and the offspring. The defect merle gene is incompletely
dominant - when a Mm carrier is bred to a non-merle mm carrier
with normal genes, still in the worst case 2 puppies out of 4 could
be expected to inherit this merle gene mutation.
Faded merle patches can sometimes be seen on newborn puppies, but
gradually disappear and are invisible after one or a few weeks. Merle
can be a common gene in different types of American bulldogs:
Follow this link address for photos of different O.E.B. merle
Look at the
light yellow chihuahua photographed on Dr. S. Schmutz' web
page about merle. It was dna-analysed to be heterozygous with
different band lengths on the alleles, 200/500 in the genotype (i.e.
probably M[c]m). The cryptic merle gene is shorter. You can't see
any merle pattern, but she could give this dominant merle gene on to her
Merle is sometimes also a
deadly, lethal defect gene - both in homozygous and
heterozygous presence - but it does not negatively affect all
carriers. It is concealed by white and light coat colours and is then
called cryptic merle in hidden carriers. It is this variety,
which causes serious problems in those dog breeds, where merle is a
desired pattern: all puppies do not survive, some can have defective
eyes or ears and defects in other vital organs, heart failures are
Dogs who are genetically
MM sometimes have one or two blue eyes - but so can also extreme
white Frenchies when they are homozygous on the S-locus, s [w]s
[w]. Even those are unfortunately often deaf, or have impaired
hearing on one or both ears. Eyes of different colour is a
disqualification in the F.C.I. breed standard for French Bulldogs -
and lightly coloured eyes is mentioned as a fault.
If any one individual carries two of the genes on the M-locus: M= merle,
M[c]= cryptic merle or m= normal non-merle gene - or else deductibly is
white on the S-locus s[w], s[p] etc. can only be detected with certainty
by a DNA analysis for merle. (A dog receiving the result mm
non-merle can in theory still have one parent carrying the Merle gene
and siblings carrying the same).
GENE AND WHITE COAT COLOUR
WITHOUT MELANIN PIGMENT CAN CAUSE
Dogs carrying the merle M gene in single or double setting - or white
coat on the S-locus - can have various defects in one or both eyes. An
eye could be abnormally small or lack some inner parts, like for
example a reflective layer called tapetum behind the retina,
which is ment to give the dog better vision in the dark.
Tapetum is formed successivly in puppies, but should
be fully developed by the age of 12 weeks.
An eye lacking the tapetum
can be detected by a camera flashlight through a dilated pupil - just
like in people (who dont't have a tapetum lucidum) - the flash will
reflect the red blood vessels behind the retina at the bottom of the
eyes. (Modern cameras automatically reduce "red eyes" though by emitting
a quick pre-flash to close the pupils just before the photo is taken,
and the flashlight then never reaches to the bottom of the eyes).
Tapetum lucidum in dogs is normally reflected by the flashlight as grey,
green, yellow or white - click to see the photos enlarged:
THE MERLE GENE AND WHITE
COAT CAN ALSO CAUSE HEARING IMPAIRMENTS - In breeding it is
equally bad, what degree of hearing impairment a dog may have, all are
equally hereditary: predominantly white Frenchies should threfore be
tested for hearing, prior to breeding. Puppies should also be
BAER tested before selling, just like Bullterriers and Dalmatians.
George Strain who developed the method recommends not to use
any sedation during the testing - it is usually not necessary and an
unnecessary cost as well as an unnecessary risk.
Better not to talk, not to see and not to listen?
French bulldogs carry the same colour genes as Boxers and Bullterriers.
All white Frenchie puppies should be BAER-tested before selling.
Ethically at least all predominantly white Frenchies should be
BAER-tested before being used in breeding. It is impossible to
detect a Frenchie deaf on one ear without a BAER-test. Half deaf
Frenchies live normal lives, but can pass deafness on to their puppies.
Almost 20% of prof. Strain's BAER-tested white Bullterriers were
deaf on one or both ears, compared to more than 1% of the coloured ones.
According to The American Boxer Club the percentages are similar.
The colour markings are the same as in French Bulldogs. White markings
are not allowed to cover more than 1/3 of the Boxer body - excess white
disqualifies Boxers from breeding and showing, according to the AKC
standard among others, although white puppies are accepted for
registration. The reason is the hearing- eye- and skin defects that are
associated with the lack of melanin (colour pigmentation).
It is an old practice among
experienced French Bulldog breeders - never to breed white and white
- and this rule of thumb is still valid today: because such
breedings earlier did result in deaf Frenchies and in Frenchies with low
vitality, who had to be euthanized at the age of one and two years old.
Likewise one should not breed white to yellow or fawn
*One must never breed
two carriers of the dominant M or M[c] toghether* - double merle
could cause organ defects and low vitality to the puppies. It is
important to dna-test possible merle carriers well in advance of a
The recessive s[w]
extremewhite-allele can give similar malformations, when inherited
double from both parents - but there is no dna-test to rule out hidden
carriers of this allele. That is why two predominantly white Frenchies
should not be mated.
In conformity with Section 11b of the German Animal Protection Act
the Board of Agruculture investigation recommends prohibition of
breedings with two merle-carriers MM or Mm because of the risk for the
various defects involved in the Merle-syndrome. Follow the link to
read the complete official investigation - search for: merle.
An even mouse gray dilute colour in coat and eyes
- yellow eyes can also be seen
Do not confuse the irregular patches of fading primary coat colour
caused by the Merle-gene with the even dilution of all the basic
colour (leaving no undiluted primary colour) caused by the
dilute-allele on D-locus, dd creating a uniform so called
blue (or a uniform gray) or very pale red, or weak yellow coat
colour - with or without ordinary white markings. This allele may cause
CDA Color Dilution Alopecia - a special kind of hair loss. This
happens when the pigment grains clump together in the presence of the
dilute d-allele, leaving the rest of the hair without any pigment so the
colour looks diluted, and causing the hairs to break easily at the root.
- This evenly blue/gray shade may be the "mouse gray" coat colour
mentioned as a disqualification in all French Bulldog breed standards.
In conformity with Section 11b of the German Animal Protection Act
the Board of Agriculture investigation recommends breeding prohibition
for dogs with a diluted blueish grey coat colour because of the defects
in the so called "Blue-dog-Syndrome". Follow the link to read the
official investigation - search for: blau.
The pied or piebald coat pattern:The s [p[ allele
was named after the magpie bird - latin: pica pica.
In pied Frenchies the more
or less brindled, black colour is clear and clean - i.e. without any
irregular faded patches of grayish blue against the medium sized white
areas. There may possibly be a few so called tickings, on the
T-locus - that is round, unfaded black dots - accepted, but not desired,
according to the French Bulldog breed standard.
Merle (French) or Merel (Germ.) means Blackbird (latin:
Turdus Merula) and they can evidently also carry the merle-mutation -
seen on this photo by the Dutch photographer Luud Riphagen.
Standard FCI N°101 / 06.04.1998 / F
the official FCI breed standard in French concerning the colours
(follow the link to the complete standard text):
Uniformément colorée fauve, bringée ou non, ou à panachure limitée.
Fauve bringée ou non, à panachure moyenne ou envahissante.
Toutes les nuances du fauve sont admises, du rouge au café au lait.
Les chiens entièrement blancs sont classés dans les "fauve bringé à
panachure blanche envahissante".
Lorsqu'un chien présentera une truffe très foncée, des yeux sombres
entourés de paupières foncées,
certaines dépigmentations de la face pourront être exceptionnellement
tolérées chez de très beaux sujets.
- Truffe de couleur autre que le noir.
- Yeux hétérochromes.
- Robe de couleur noir et feu, gris souris, marron.
Word for word translation of the original French text in the FCI
Uniformly coloured fawn, brindled or not, or with limited markings.
Fawn brindled or not, with medium or overflowing markings.
All shades of fawn are admitted, from red to café au lait.
Entirely white dogs are classified among "brindled fawn with overflowing
When a dog presents a very dark nose, dark eyes, surrounded by dark rims
on the inner lids,
a few pigment losses in the face can exceptionally be tolerated in very
- Nose of colour other than black.
- Eyes of different colours.
- Coat colours black and fire, mouse grey, chestnut brown.
'Baby fallow deer-coloured' coat, in French 'fauve' and in English
'fawn' is thus regarded as the primary colour in the breed. All shades
of fawn are allowed in the breed standard, from red to 'coffee with
Evidently, a French Bulldog may not according to the breed standard
carry both black/brown and yellow/red areas in the coat, because "black
and fire" is mentioned among Disqualifying faults. Those ever
more frequent tricoloured Frenchies with yellow, black and white coat
colour patches should consequently not be award winners in shows.
In colour genetics this fawn colour is called agouti, 'tan' or
'sabel' and is described as the allele a(y) =yellow. Dogs have a
mixture of brown/black and red/yellow pigment grains in their coats -
and the alleles on A-locus in the chromosome influence on how this is
expressed in each dog. Agouti-locus codes for the distribution of
pigment, both in the individual hair and in the entire coat. There is an
interaction between black/brown pigment (eumelanin) and red/yellow
pigment (phaeomelanin). The regulation of how the two are expressed is
conducted by the agouti protein.
The coat colour pigments may according to the breed standard be visible
in streaks - brindle - or without brindling. Recent observations by
Barsh, Murphy, Schmutz et al. place the
brindle gene on the K-locus, which regulates the distribution of
black/brown pigment. Uppermost in this series is K, which codes for
dominant black/brown pigment, without any visible red/yellow pigment
being expressed. Its allele k(br) - brindling creates black
streaks on a yellow/fawn background. Only dogs genetically carrying
the allele for agouti, yellow/red a(y) can display brindle streaks
on the entire body. The inheritance of brindle has been disputed. From
the beginning Dr. C.C. Little placed the gene for brindle in the
E-series for Extension, as the allele e(br) - which could also be
expressed only in the presence of the allele for yellow, a(y).
The coat may also according to the breed standard have more or less
extended white markings - which totally lack colour pigments. These
pigment free white markings (fr. 'panachure') can be totally absent (the
S-locus for solid colour, i.e. with no white markings) - or be present
to various extent under the influence of three alleles: either small,
medium or overflowing markings, as in entirely white dogs, which
consequently lack colour pigments in their coat and skin. This genetic
fact is also made clear in the French standard text, above - but this
has frequently been misunderstood and misinterpreted.
In genetics a
uniform, solid coat colour - without any white markings, as in the Pug -
is characterized by the letter S.
White markings i.e.various extensions of areas without pigments are
characterized by the alleles:
S(i) = small white markings - as in the Irish rat, and in Boston
S(p) = medium white markings - as in the Magpie bird, and in pied
S(w) = overflowing white markings - extreme white, as in entirely white
N.B. Please note that:
- white is not a
colour in French Bulldogs, white is more or less extended
markings in a haphazard pattern without any colour pigment.
- The basic yellow/red or black/brown pigment colours in the breed
should never be regarded as markings - they are the primary coat
colour, even when white markings (without any pigment) are overflowing
in pied s[p] or extreme whites s[w] Frenchies.
NOTE: black-and-tan, fr. noir-et-feu, is a disqualifying colour
S(p) A piebald or pied French Bulldog has a black/brown or
yellow/red coat colour, with or without brindle stripes - and medium
sized white markings.
S(w) An extreme white French Bulldog has overflowing white
markings - and its black/brown or yellow/red coat colour may be visible
only on small, insignificant patches in the coat.
The transcription factor MITF, which may cause various malformations in
the eye, can be detected in
all tested dogs, carrying the alleles for piebaldism, those with
medium sized white markings s(p) and the ones with overflowing white
markings s(w) extreme white, also called extreme piebald.
MITF has not been detected in dogs with solid coat colour without white
markings (S), and not in dogs with small white markings in the allele
Responsible breeding should
avoid mating predominantly white Frenchies with each other, and also
Frenchies both having predominantly white close relatives, like parents
and siblings. The reason is that att the absence of pigmentation in
itself predisposes for skin problems and defects in ears and eyes - as
PHOTO SURVEY OF ALL COAT COLORS AND MERLE PATTERNS
IN BULLDOG VARIETIES - HAMMERHEAD KENNELS U.S.A.:
Olde English Bulldogge