A5: Principle horse coat colour and markings, their inheritance. Flashcards
name x3 principal coat colours
bay
black
chestnut
name modified variants of coat colours
grey
roan
what coat colours are breed characteristic?
Suffolk Punch: chestnut
Cleveland Bay
Fresian: Black
what rules are valid for coat colour?
Rules of Mendelian Inheritance are valid for coat colour.
example: roan: intermediate inheritnace.
what genes control colour inheritance?
A, E, G, R, W, C.
Pigment synthesis determined by gene loci (1):
what is the protein and gene locus?
what does it effect?
TYRP1 = Tyrosine Kinase Protein
gene locus = B
B: black eumelanin, b: brown eumelanin
Pigment synthesis determined by gene loci (2):
what is the protein and gene locus?
what does it effect?
ASIP = Agouti-signal protein (binds to MC1R)
gene locus = A
AA, Aa: eumelanin (black) in long hairs, but pheomelanin (brown) in short hairs.
At and a: mutant alleles
AA: light BAY,
AAt: medium BAY,
AtAt: dark BAY
aa: long and short hairs, skin, eyes and hooves are also black –> BLACK
Agouti gene controls distribution of black coloured hair
Pigment synthesis determined by gene loci (3):
what is the protein and gene locus?
what does it effect?
E = melanin extension or non-extension.
E: tyrosinase-activity and normal MC1R - activity lead to dark, black pigments.
e - mutant: low tyrosinase activity and abnormal MC1R activity lead to reddish, yellowish pigments.
EE, Ee: ability to produce eumelanin (black) in skin and hair; only in long hairs (BAY, BROWN) or everywhere (BLACK);.
ee: pheomelanin (red) in long and short hairs, skin and hoof also pigmented but lighter (CHESTNUT, RED, SORREL). skin is black but hair pigment appears red.
Extension of red pigments (red, chestnut, sorrel).
Pigment synthesis determined by gene loci (4):
what is the gene locus?
what does it effect?
“C” tyrosinase locus
C: tyrosinase activity,
c: defect in tyrosinase activity - albinos
Pigment synthesis determined by gene loci (5):
what is the gene locus?
what does it effect?
g: normal,
G: mutant, responsible for the malignant melanoma and vitiligo formation. Melanomas are twice more common in GG than in Gg genotypes.
When tyrosinase is overproduced,
hyperpigmentation occurs in the form of an
increasing number of dark spots on the skin (moles, freckles), from which melanoma forms.
what does the grey gene do?
Excludes colour pigment from hair over time.
Foal born dark grey (will look black), by the time the animal is 6-8 years old they can be light grey (looks white)
Pigment synthesis determined by gene loci (9):
what is the gene locus?
what does it effect?
Rn, rn, roan, co-dominant, intermediate inheritance: a nearly even or variable mixing of coloured (black, brown, yellow and red) and white hairs. On branding site dark (pigmented) hairs!
RnRn, Rn/rn: - bay (purple, classic) roan,
- black/blue roan,
- red/chestnut/strawberry roan. rn: no roan
Appaloosa characteristics may be related to roan gene D –> Dilution/ dominant
Pigment synthesis determined by gene loci (7):
what is the gene locus?
what does it effect?
D gene location: responsible for melanin
distribution in hairs.
A dilution gene will create a lighter coat colour.
Dun gene is a dilution gene that affects both red and black pigments in coat colour.
DD or Dd: classical dun colours - mouse dun, brown/bay, and red/chestnut dun; many other variations: blue- yellow-, orange-, red-, apricot-, silver-dun, wild colours, modifier: cremello allele.
Plus primitive markings: eel (dorsal line) and zebra stripes
Pigment synthesis determined by gene loci (6):
what is the gene locus?
what does it effect?
W = white gene
inability to form pigment.
WW: embryonic lethal, the dominant homozygous genotype dies in embryonic age due to pigment cell death.
Ww: white horses, no pigment in skin and hair, possible in eyes, born white too;
ww: pigmented, different colour
Note leucism + albinism
* Leucismis a condition in which there is (partial) loss of pigmentation in an animal resulting in white, pale, or patchy coloration of the skin, hair, feathers, scales or cuticle, but not the eyes. Unlike albinism, it is caused by a reduction in multiple types of pigment, not just melanin.
Pigment synthesis determined by gene loci (8):
what is the gene locus?
what does it effect?
C = colour/albino, tyrosinase or cream gene locus.
Membrane associated transporter protein (MATP): mediates melanin synthesis, probably transports molecules necessary for the normal function of melanosomes.
CC: fully pigmented.
CCcr: from red pigment light yellow dilution, black pigment fades (less affected),
from bay –> BUCKSKIN and lighter, washed colours,
from black –> SMOKEY,
from chestnut –> PALOMINO (golden).
CcrCcr: both red and dark pigments are diluted, from bay, black and –> chestnut PERLINO, SMOKEY CREAM and CREMELLO (pseudoalbinos)
