dog coat colour

Question 1

why coat colour

Answer 1

-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

Question 2

side effects of domestication syndrome

Answer 2

-smaller brain size
-shortened snout
-weakened ear cartilage
-tail cartilage shortening/curling
-reduced tooth size

Question 3

what are melanocytes

Answer 3

cells that sit at the base of the hair follicle and give rise to colour

Question 4

what are the two melanin pigments

Answer 4

-phaeomelanin (red, yellow, cream)
-eumelanin (black, brown, grey)

Question 5

dog coat colour genetics

Answer 5

-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

Question 6

dominant/recessive

Answer 6

-dominant is black which is phenotypically displayed if present
-recessive is red and is phenotypically displayed if in the homozygous state

Question 7

co dominant traits

Answer 7

heterozygote has different phenotypes

Question 8

dominance hierarchy

Answer 8

one mutation has stonger effects then another

Question 9

compound heterozygotes

Answer 9

two different mutant alleles at a
particular gene locus, one on
each chromosome

Question 10

epistasis

Answer 10

alleles at one locus mask
expression of alleles at another
locus

Question 11

E Locus = Extension locus
(MC1R)

Answer 11

▪ Melanocortin Receptor 1 (MC1R)
▪ Melanocyte stimulating hormone (MSH)
▪ EM > EG > E > (ea)>e

Question 12

What is the role of MC1R?

Answer 12

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.

Question 13

e Allele at MC1R

Answer 13

-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

Question 14

e/e genotype

Answer 14

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)

Question 15

EM Allele of MC1R

Answer 15

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

Question 16

Grizzle EG

Answer 16

▪ 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

Question 17

Grizzle in sluki and afgan

Answer 17

▪ 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

Question 18

Northern Domino (eA)

Answer 18

▪ 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)

Question 19

A locus = ASIP

Answer 19

• 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)

Question 20

ASIP - aw

Answer 20

• Banded/Sable (aw) is the “wild type”
• Occurs in wolves and coyotes - the “wild” standard
• “fixed”
  banded hairs on
  most of the dorsal
  surface

Question 21

ASIP - ay

Answer 21

▪ 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

Question 22

ASIP - at

Answer 22

▪ Black-and-tan, black with tan points, or tricolor
▪ at is caused by a promoter mutation in ASIP

Question 23

ASIP- a

Answer 23

-recessive black (a) is cause by a premature stop codon
-rare mutation
-all black german shepherd dogs and shelties and gronendaels
-som herding breeds

Question 24

saddle tan

Answer 24

-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