dog coat colour Flashcards
why coat colour
-hallmark traits in most breed standards
-easily observed/recorded (involve breeders in research and students in teaching
-because melanoblasts and neuroblasts derive from the same progenitor cells, there are important development issues
side effects of domestication syndrome
-smaller brain size
-shortened snout
-weakened ear cartilage
-tail cartilage shortening/curling
-reduced tooth size
what are melanocytes
cells that sit at the base of the hair follicle and give rise to colour
what are the two melanin pigments
-phaeomelanin (red, yellow, cream)
-eumelanin (black, brown, grey)
dog coat colour genetics
-interactions amongst different loci
-dogs may have a particular genotype at one locus and yet not exhibit the expected phenotype because of an incompatible genotype at another locus
dominant/recessive
-dominant is black which is phenotypically displayed if present
-recessive is red and is phenotypically displayed if in the homozygous state
co dominant traits
heterozygote has different phenotypes
dominance hierarchy
one mutation has stonger effects then another
compound heterozygotes
two different mutant alleles at a
particular gene locus, one on
each chromosome
epistasis
alleles at one locus mask
expression of alleles at another
locus
E Locus = Extension locus
(MC1R)
▪ Melanocortin Receptor 1 (MC1R)
▪ Melanocyte stimulating hormone (MSH)
▪ EM > EG > E > (ea)>e
What is the role of MC1R?
MC1R gene provides instructions for making a protein called the melanocortin 1 receptor. This receptor plays an important role in normal pigmentation. The receptor is primarily located on the surface of melanocytes, which are specialized cells that produce a pigment called melanin.
e Allele at MC1R
-317 amino acids long
-* “E” allows both eumelanin and phaeomelanin to be
produced
* Mutation in DNA at position 914 C>T results in protein
termination at amino acid 306 (p.R306ter)
* “e” causes “clear red” because the receptor has a
premature stop codon
e/e genotype
Dogs that are e/e do not have a single black or brown hair
on them!
They are “clear red”.
e/e is epistatic (masks) other alleles at A (Agouti) and K
(beta defensin)
EM Allele of MC1R
Melanistic Mask (frencie)
Why the face & ears? Highest
concentration of pigment/neural
cells
* Not visible on solid black dogs or
dogs with a white mask
EM Allele of MC1R
Grizzle EG
▪ In two “old” breeds, Saluki and Afghan
Hounds, a pattern exists that does not
occur in other breeds
▪ The pattern includes a grizzled dorsal
surface
Grizzle in sluki and afgan
▪ facial marking is considered a hallmark of this pattern
Grizzle (Saluki)- E locus: EG/_
A locus: atat
Domino (Afghan)- E locus: EG
A locus: atat
Black-and-tan (saluki)- E locus: E/_
A locus: atat
Black-and-tan (afghan)- E locus: E/_
A locus: atat
Northern Domino (eA)
▪ R301C mutations in MC1R has been observed in different
dog breeds, but with unknown consequence
▪ This mutation found in archeological dog specimens over
10,000 years old not found in any wolf samples or “wolf-
like” ancient specimens (Anderson et al 2020)
▪ Found in 1.5% of dogs genotyped (12,000 dogs sampled)
and all Alaskan Malamute dogs tested
▪ Not in the Asian Spitzes (e.g. Shiba Inu, Akita)
A locus = ASIP
- Agouti Signalling
Protein - Multiple Alleles
- Dominance Hierarchy
ay > aw > at > a - New mutations found
recently - Dreger et al 2020
- Banasch et al 2021
-eumelanin and pheomelanin found in the same hair (alternating)
ASIP - aw
- Banded/Sable (aw) is the “wild type”
- Occurs in wolves and coyotes - the “wild” standard
- “fixed”
banded hairs on
most of the dorsal
surface
ASIP - ay
▪ Fawn or sable (note nomenclature is
inconsistent among breeds)
▪ “mostly reddish”, but some hairs can be
black
▪ Some red hairs can have black tips
-also shaded sables
ASIP - at
▪ Black-and-tan, black with tan points, or tricolor
▪ at is caused by a promoter mutation in ASIP
ASIP- a
-recessive black (a) is cause by a premature stop codon
-rare mutation
-all black german shepherd dogs and shelties and gronendaels
-som herding breeds
saddle tan
-saddle tan and black and tan both give genotype atat at agouti signalling protein (ASIP)
-what is the additional gene or mutation for saddle tan?
-saddle tan is a modification of black and tan to get saddle tan the animal must be black and tan atat and agouti locus
-the dominant allele at RALY causes saddle tan
what genotypes give you grizzle
EG/EG; EG/E; EG/e
what is a melanistic mask
EM/_
what is the phenotype of e/e
clear red ie. Irish setter
what is the wild type of ASIP
aw
what is the dominant of ASIP
ay sable or fawn
what does atat look like
black and tan
dom hierarchy of ASIP
ay, aw, at, a
what is a for ASIP
responsible for balck dogs in herding breeds
K locus
-KB, KBr, Ky
-uses beta-defensin 103
-can get eumelanin if you have a working receptor
-KB allele negates expression of phaeomelanin (red) pigment form ASIP
black genotypes
-there are two that cause SOLID black
-a few breeds can have both genotypes
-most non herding breeds: KB/, E/
-herding breeds: a/a
brindle
-KBr
-KB, KBr, Ky
-gene causing spacing
-alternating eumelanin and phaemelanin
-light brindling, heavy brinding, reverse brindling
B locus
-TYRP1
-3 mutations causing brown bc, bd, and bs
-4th mutation found in 2018
-S41C, Try185ter, Q331er, 345delP
B locus and skin
-all have brown nose and pads
-if not brown they’d be black
-doesn’t affect pheomelinin
cocoa colouring
-in franchies
-its not black its just a really dark brown
-HPS Co/Co TYRP b/b
MC1R + TYRP1
-“red” dogs e/e homozygous for TYP1 mutations b/b have brown noses and pads
-“red” dogs e/e with wild type TYRP1 allele (B) have black noses and pads
D Locus
-melanophilin (MLPH)
-grey or blue colour recessive (dd)
-mutation found in MLPH gene
-three mutations currently identified
-d1 (more common)
-d2 (sloughi, chow chow, and thai ridgeback)
-d3 (rare)
-affects both eumelanin pigments black and liver
if you have a black dog and it has bb what colour is it
brown
if you have a black or brown dog with dd what colour are they
one is blue and the other is lilac
what does the D locus affect
both eumelanin pigments black and liver
M locus
-PMEL or SILV
-premelanosome protein (silver locus)
-MM (deaf) microphthalmia and anophthalmia
-Mm (merle)
-mm not merle
merle- PMEL (SILV)
-short interspaced nuclear element is inserted in the gene disrupting the function
-thymine (T) nucleotide number varies
-T (54-65) not merle
-T (90-101) + SINE=all merle dogs studied thus far
-harder to see in fawn/sable dogs
-e/e is epistatic to merle
harlequin spotting- PSMB7
-gene: proteosome beta 7
-one H and M allele required
-H/H is fetal lethal
-unique to great dane
-H/h, M/m
-merle but when not a black spot its white
what is white
not a colour but the absence of colour
what could cause a purebred lab to have white on chest
-melanocytes just didn’t reach that area
-can happen if the bitch is sick during pregancy
S locus-MITF
-melanocyte inducing transcription factor (MITF) of microphthalmia- associated transcription factor
-MITF has been reported to cause spotting in some breeds
-SINE insertion resulting in piebald (sP)
-SS-regular
-SsP-minor white markings
-sPsP-major white markings, amy be deaf
irish spotting
-Bernese, Australian shepherd
-equal on both sides (symmetrical)
-sisi
panda white spotting
-german shepherd
-autosomal dominant mutation “P”
-embryonic lethal
-mutation in KIT spotting gene
In locus- intensity
-in many breeds e/e dogs are cream to white instead of red
-these dogs are “fixed” for a paling genotype or intensity genotype
-mutation found in MFSD12 gene in golden retrievers and yellow labs
-KITLG mutation causes shades of phaeomelanin
In locus- intensity cream/ white
-samoyeds have been genotyped as e/e and a/a
-the melanocytes can produce pigment
-a allele found only in herding breeds
albinism- C locus- SLC45A2
-visual acuity comprosed
-albinism in other animals caused by tyrosinase
-SLC45A2 mutations- caz, cal
ticking and roan
-ticking spots/flecks of colour on white (T)
-roan is mottled white areas
-ticking more on legs and muzzle, while roan is more even over body
-gene not known
-ticking and roan may be alleles of the same gene
-can look like Merle but this is colour coming through white
