{{Short description|Genetic pattern in a dog's coat}} {{Multiple issues| {{more citations needed|date=September 2011}} {{lead too short|date=April 2012}} }} [[File:BorderColliePupTheEye wb.jpg|thumb|Blue merle [[Border Collie]] puppy with [[Heterochromia|odd-colored eyes]]]] [[Image:AussieRedmerle01.jpg|thumb|Red merle [[Australian Shepherd]]]]
'''Merle''' is a genetic pattern in a [[dog]]'s [[Coat (dog)|coat]] and [[allele|alleles]] of the [[PMEL gene]]. It results in different colors and patterns and can affect any coats. The allele creates mottled patches of color in a solid or [[piebald]] coat, blue or [[Heterochromia|odd-colored eyes]], and can affect skin [[pigment]] as well. Two types of colored patches generally appear in a merle coat: brown/liver (red merle) and black (blue merle). Associated breeds include [[Carea Leonés]], [[Australian Shepherd]]s and [[Catahoula Leopard Dog]]s. Health issues are more typical and more severe when two merle-patterned dogs are bred together.
== Description == Merle can affect all coat colors. The merle forms of brown are usually called "red" (though this is not correct; red and brown are genetically different), and black is called "blue" as lighter patches of black are formed throughout the coat and look slightly blue in color. Dogs who are recessive red can still be affected by merle, but the patches are either hardly seen or, if the dog is a clear recessive red, are not visible at all.<ref>{{cite web|last=Schmutz|first=Sheila|title=Schmutz - Merle coat color genetics|url=http://homepage.usask.ca/~schmutz/merle.html|publisher=Sheila Schmutz|access-date=28 October 2011}}</ref><ref name=":0">{{cite web|last=Presberg|first=Carole|title=Recessive Red Merle Border Collie|url=http://www.gis.net/~shepdog/BC_Museum/Permanent/BCColors_Merle/BC_ColorBlueMerle.html|publisher=Carole Presberg|access-date=28 October 2011|archive-url=https://web.archive.org/web/20111121225810/http://www.gis.net/~shepdog/BC_Museum/Permanent/BCColors_Merle/BC_ColorBlueMerle.html|archive-date=21 November 2011}}</ref> Combinations such as [[brindle]] and sable merle exist, but are not typically accepted in [[Breed standard (dogs)|breed standards]].<ref name=":0" />
In addition to altering the base coat color, merle also modifies eye color and coloring on the nose and paw pads. The merle allele modifies the dark pigment, resulting in eyes or [[Heterochromia|parts of eyes]] turning blue. Since merle causes random modifications, dark-eyed, blue-eyed and [[Heterochromia|odd-colored eyes]] are possible.<ref>{{cite web|last=McDonald|first=Lisa|title=Aussie Eye Color|url=http://www.ashgi.org/color/aussie_eye_color.htm|publisher=Lisa McDonald|access-date=28 October 2011|archive-url=https://web.archive.org/web/20111007114652/http://www.ashgi.org/color/aussie_eye_color.htm|archive-date=7 October 2011}}</ref> Pigmentation on paw pads and nose may be mottled by pink.<ref>{{cite web|title=Merle Coat, mottled paw pads|url=http://perfectpekskennel.com/MerleCoat.aspx|publisher=Perfect Peks Kennel|access-date=28 October 2011|archive-url=https://web.archive.org/web/20110303120251/http://perfectpekskennel.com/MerleCoat.aspx|archive-date=3 March 2011}}</ref>
== Breeds == Merle is a distinguishing marking of several breeds, particularly the [[Australian Shepherd]] and [[Catahoula Leopard Dog]], and appears in others, including the [[Miniature American Shepherd]], the [[Koolie]] in Australia, the [[Shetland Sheepdog]], various [[collie]] breeds, the [[Welsh Corgi (Cardigan)|Cardigan Welsh Corgi]], the [[Pyrenean Shepherd]] and the [[Bergamasco Shepherd]].<ref name="americanspanielclub.org">{{cite web|title=Merle Color in Cocker Spaniels |last=Born |first=Charles |url=https://www.americanspanielclub.org/about-the-breed/merle-color-in-cocker-spaniels/|publisher=American Spaniel Club|access-date=20 April 2018}}</ref> In [[Dachshund]]s, the merle pattern is known as "dapple".<ref>{{cite web|url=http://www.dachshund.org/article_double_dapple.html |title=The Double Dapple |publisher=The Dachshund Magazine Online |access-date=June 25, 2007 }}</ref> In [[Beauceron]]s the merle pattern is known as "harlequin". The merle allele also plays a part in producing harlequin [[Great Dane]]s. Depending on the breed, registry or country, the pattern may be register-able with a [[Breed registry|registry]] but not allowed in [[Conformation show|conformation]], and the pattern may not be recognized by the [[breed standard]], disqualifying it from [[Conformation show|showing]].<ref>{{cite web|title=Chihuahua Club of Canada - Merle Breeding Ban |url=http://chihuahuaclubofcanada.ca/merle-breeding-ban|publisher=Chihuahua Club of Canada|access-date=20 April 2018}}</ref><ref name="americanspanielclub.org"/> There may also be additional requirements for the pattern such as the dog being allowed to have the pattern but must have completely dark eyes with no blue in them.<ref>{{cite web|title=Pomeranian Colors - Any other allowable color |last=Born |first=Charles |url=http://www.americanpomeranianclub.org/colors/aoac.htm|publisher=American Pomeranian Club|access-date=20 April 2018}}</ref>
Merle is sometimes introduced to other [[purebred]] dog breeds through [[crossbreeding]] such as [[French Bulldog]]s, [[Poodle]]s and even [[American Bully|American Bullies]], but these dogs are not purebred. In 2020 the UK Kennel Club (the oldest in the World) banned the registration of merle Poodles as it is not and never has been a colour pattern recognised in pure Poodles by the club.<ref>[https://www.thekennelclub.org.uk/press-releases/2020/january/registration-of-dogs-of-merle-colouring/ Registration of dogs of merle colouring] 9 January 2020 ''www.thekennelclub.org.uk'' accessed 20 March 2021</ref>
== Genetic basis == [[File:Merle Dog.png|thumb|[[Punnett square]] showing potential consequences of breeding two merle dogs together<ref>Jess Chappell: [http://www.doggenetics.co.uk/merle.html#double Dog Coat Colour Genetics: Doppel-Merle] ''www.doggenetics.co.uk''</ref>]] The merle allele is actually an [[incomplete dominance|incompletely dominant]] [[allele]].<ref>{{cite web|last=Sheila|first=Schmutz|title=Schmutz – Merle|url=http://homepage.usask.ca/~schmutz/merle.html|publisher=Sheila Schmutz|access-date=27 October 2011}}</ref> If two [[heterozygote]] merle dogs are mated, on the average, one-quarter of the puppies will be "double merles", which is the common term for dogs homozygous for the longest versions of the merle alleles,<ref>{{cite web|title=White Aussies Brochure|url=http://www.lethalwhites.com/brochure/WhtAusBro.pdf|publisher=White Aussies Project|access-date=27 October 2011}}</ref> and a high percentage of these double merle puppies could have eye defects or be deaf. Knowledgeable and responsible breeders who want to produce merle puppies mate a merle with a non-merle dog; roughly half the puppies will be merles, and none will have the vision or hearing defects associated with double merle dogs.<ref>{{cite web|title=Double Merle|url=http://www.lethalwhites.com/doublemerle.html|publisher=White Aussies Project|access-date=27 October 2011}}</ref>
In January 2006, scientists at [[Texas A&M University]] announced the discovery of a mobile genetic unit called a [[retrotransposon]], responsible for the various merle mutations in dogs.<ref name="transposon"/> Merle can be tested for and identified through DNA.<ref>{{cite web|title=UC Davis – Merle genetic testing|url=https://www.vgl.ucdavis.edu/services/dog/Merle.php|publisher=UC Davis|access-date=20 April 2018}}</ref>
A '''cryptic merle''' is one with such small patches of merling, or none at all, that it appears to be a non-merle.<ref name="coile">{{Cite book |last=Coile |first=D. Caroline |title=Australian Shepherds |year=1999 |publisher=Barron's |isbn=978-0-7641-0558-6 |pages=[https://archive.org/details/australianshephe0000coil/page/20 20–21] |chapter=Obtaining an Australian Shepherd |chapter-url=https://archive.org/details/australianshephe0000coil/page/20 }}</ref> This is commonly seen in dogs who are recessive red, clear recessive reds in particular, though patches can still be seen in certain red dogs.<ref>{{cite web|last=Schmutz|first=Sheila|title=Schmutz – Merle|url=http://homepage.usask.ca/~schmutz/merle.html|publisher=Sheila Schmutz|access-date=27 October 2011}}</ref> In America, a dog with the phantom merle coloring is sometimes described as being "cryptic for merle". A cryptic merle bred to a merle may produce merles, cryptic merles or non-merles, depending on whether the parents were heterozygous or homozygous for the merle alleles.<ref>{{cite web|title=Cryptic Merles|url=http://www.ashgi.org/home-page/genetics-info/coat-color/cryptic-merles|publisher=ASHGI|access-date=20 April 2018}}</ref> Another mutation for cryptic merle has been identified by Dr. Helena Synková, and has been given the working name of "atypical merle". It is recommended that if a breeder is unsure if their dog is merle or not, that they be tested for the merle allele lengths.<ref name="americanspanielclub.org"/>
== Modifiers == Certain modifying genes work in tandem (co-dominant expressive) with the merle alleles to create a completely different look to the pattern.
Often mistaken for a "double merle", a '''harlequin merle''' (or just harlequin), is a [[Great Dane]] that carries both the merle pattern allele and the co-dominant modifying gene for harlequin, PSMB7 (also known as H). This causes most or all of the diluted "blue" color to be replaced with white, resulting in a dog that is mostly white with black patches. All dogs exhibiting the harlequin pattern also have the merle allele. Found only in [[Great Danes]], (and registered as Harlequin).<ref name="doggenetics.co.uk">{{cite web|url=http://www.doggenetics.co.uk/harlequin.html|title=Dog Coat Colour Genetics|work=doggenetics.co.uk}}</ref>
In 2018, a published paper identified six general categories of merle alleles that affect (or do not affect) the final coat color depending on the length of the SINE insertion within them.<ref>{{cite journal |last1=Langevin |first1=Mary |last2=Synkova |first2=Helena |last3=Jancuskova |first3=Tereza |last4=Pekova |first4=Sona |title=Merle phenotypes in dogs – SILV SINE insertions from Mc to Mh |journal=PLOS ONE |date=20 September 2018 |volume=13 |issue=9 |article-number=e0198536 |doi=10.1371/journal.pone.0198536 |pmid=30235206 |pmc=6147463 |bibcode=2018PLoSO..1398536L |language=en |issn=1932-6203|doi-access=free }}</ref>
== Health issues == Dogs with two copies of some versions of the merle allele (called "double merle") have an even higher probability of being deaf and with vision impairments.<ref>{{cite journal|last=Strain|first=GM|author2=Clark LA |author3=Wahl JM |author4=Turner AE |author5=Murphy KE. |title=Prevalence of deafness in dogs heterozygous or homozygous for the merle allele|journal=Journal of Veterinary Internal Medicine|date=3 March 2009|volume=23|issue=2|pages=282–6|pmid=19192156|doi=10.1111/j.1939-1676.2008.0257.x|citeseerx=10.1.1.693.7956}}</ref> The UK [[Kennel Club]] has acknowledged the health risk associated with these particular homozygous merles and stopped registering puppies produced from merle to merle matings in 2013. Merle to merle mating is currently only forbidden in three breeds.<ref>{{cite web|title=Merle to merle mating in dogs|url=http://www.thekennelclub.org.uk/item/4303|publisher=The Kennel Club|access-date=7 September 2012|date=18 May 2012|archive-url=https://web.archive.org/web/20120701125634/http://www.thekennelclub.org.uk/item/4303|archive-date=1 July 2012}}</ref>
The suppression of pigment cells ([[melanocytes]]) in the iris and in the [[stria vascularis]] of the [[cochlea]] (inner ear) leads to blue eyes and deafness. An auditory-pigmentation disorder in humans, [[Waardenberg syndrome]], reflects some of the problems associated with homozygous merle dogs and genetic research in dogs has been undertaken with the goal of better understanding the genetic basis of this human condition.<ref name=transposon>{{cite journal|last=Clark|first=LA|author2=Wahl JM |author3=Rees CA |author4=Murphy KE |title=Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog|journal=Proc. Natl. Acad. Sci. U.S.A.|date=31 Jan 2006|volume=103|issue=5|pages=1376–81|pmid=16407134|doi=10.1073/pnas.0506940103|pmc=1360527|doi-access=free}}</ref>
<gallery widths="200px" heights="200px"> File:Aussie double merle.jpg|A deaf eight-month-old homozygous merle [[Australian Shepherd]]. She has blue eyes with starburst pupils and an eccentric pupil in her left eye. File:Dogge Merle homozygot.jpg|A [[Great Dane]] mix homozygous for merle displaying bilateral [[microphthalmia]] File:Doppel Merle.png|An [[Australian Shepherd]] homozygous for merle </gallery>
=== Ocular defects === Dogs who are homozygous for certain merle alleles often have visual and auditory deficits.<ref name="coile"/> These dogs are sometimes referred to as "double merle" and sometimes incorrectly referred to as "lethal white". Ocular defects include [[microphthalmia]], conditions causing increased ocular pressure and [[colobomas]], among others.<ref name=genomics>{{cite book|title=Genomics of Disease|url=https://archive.org/details/genomicsdiseases00gust|url-access=limited|year=2008|isbn=978-0-387-76722-2|page=[https://archive.org/details/genomicsdiseases00gust/page/n96 81]|editor=Gustafson, JP|display-editors=etal}}</ref> Double merle dogs may be deaf or blind or both, and can carry ocular defects in blue or colored eyes.<ref name=eyes>{{cite web|title=Eye defects in Australian Shepherds|url=http://www.ashgi.org/color/eyedefects.htm|access-date=16 April 2011}}</ref> Currently no studies have been done to prove whether or not the merle gene affects the eyes, causing blindness.
=== Auditory defects === In one study of 38 dachshunds by a German researcher, partial hearing loss was found in 54.6% of double merles and 36.8% of single merles. One out of the 11 (9.1%) double merles was fully deaf while none of the single merles were.<ref name="George Strain on Merle"/> Another study done by [[Texas A&M University]] found that of 22 double merles, eight were completely deaf and two were deaf in one ear. Of 48 single merles, one was deaf in one ear and none were completely deaf.<ref name="George Strain on Merle">{{cite web|title=George Strain on Merle|url=http://www.merlepoms.org/Articles/George%20Strain%20on%20Merle.pdf|publisher=Merle Poms|access-date=27 October 2011}}</ref> In another study of 70 dogs, 15 of them Catahoula Curs, 4 of the Catahoulas were deaf, while 86% of the double merles of other breeds were deaf.<ref name="George Strain on Merle"/>
Deaf and/or blind dogs can live well with proper care. Various internet groups are dedicated to supporting carers of such dogs. Deaf dogs can compete successfully in agility.<ref name=agility>{{cite web|title=Deaf Dogs Roundtable|url=http://agilitynet.co.uk/training/deaf_roundtable.HTML|access-date=16 April 2011}}</ref> {{clear}}
== See also == * [[List of dog coat patterns]]
== References == {{Reflist|2}}
== External links == {{Commons|Merle (coat colour in dogs)|Merle (coat colour in dogs)}} * [https://web.archive.org/web/20070103220318/http://homepage.usask.ca/~schmutz/merle.html Merle dog coat color genetics] * [https://www.lsu.edu/deafness/deaf.htm Deafness in Dogs and Cats] * [http://www.lethalwhites.com/ White Aussies Project] * [http://bowlingsite.mcf.com/Genetics/Merle.html Genetics of merle dogs] * {{cite web|url=http://asca.org/About+Aussies/Color-Basic+Info |title=Basic Body Colors of the Australian Shepherd |access-date=2007-05-15 |author=ASCA |archive-url=https://web.archive.org/web/20070408065431/http://www.asca.org/About%2BAussies/Color-Basic%2BInfo |archive-date=2007-04-08 }}: Basic, simple-language explanation of Australian Shepherd merle colorings * [http://www.australian-shepherd-lovers.com/lethal-white.html Homozygous "Lethal White" Merles] * [http://www.border-wars.com/tag/double-merle Border Wars - Double Merle Articles] * [http://www.chihuahuaclubofcanada.ca/merle-breeding-ban Banning of Merle 'pattern' Chihuahua in Canada] * [https://catahoula-coat-color-genetics.webnode.com/merle/ Catahoula Coat Color Genetics - Introduction and History of Merle] * [https://www.americanspanielclub.org/about-the-breed/merle-color-in-cocker-spaniels/ Merle Color In Cocker Spaniels]—The American Spaniel Club
{{DEFAULTSORT:Merle (Coat Colour In Dogs)}} [[Category:Animal coat colors]] [[Category:Animal hair]] [[Category:Dog anatomy]]