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Horse Systems and Management > Coat Color Genetics > Flashcards

Coat Color Genetics Flashcards

1
Q

what kind of trait is coat color and why?

A

qualitative; even though there are so many genes involved it still can be put into categories

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2
Q

what are the 2 starting point options for coat color for horses that all other genes only modify?

A

black or red

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3
Q

how are genes named? (2)

A
  1. in reference to their role in a biological pathway
  2. for the disease/condition in which they were first associated
    all with no clear association with the particular phenotype
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4
Q

what is the longer name for gene E?

A

MCR1

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5
Q

what is gene E? (2)

A
  1. the extension gene
  2. determines if horse is red or black
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6
Q

what is dominant and recessive for gene E?

A

black is dominant (E)
red is recessive (ee)

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7
Q

does gene E determine pattern or placement of black pigment on a horse?

A

no; that is up to other genes

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8
Q

as controlled by genes OTHER than E, where can black hairs be found on a horse? (2)

A
  1. either in a distinctive pattern on the points (legs, mane, tail)
  2. or all over the entire body
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9
Q

what is the phenotype of EE or Ee?

A

black pigment in hair and skin

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10
Q

what is the phenotype of ee?

A

horse has black pigment in skin, but hair pigment appears red

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11
Q

describe the range of coat colors from ee (3)

A
  1. some shade of red, with NO black points
  2. ranging from liver chestnut to dark chestnut to chesnut or sorrel
  3. may have mane and tail that are dark red or brown
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12
Q

describe EE (4)

A
  1. no red factor detected
  2. cannot have red foals, regardless of the color of the mate
  3. base color is black, bay, or brown
  4. includes buckskin, zebra dun, grullo, perlino, gray, tobiano, overo, roan, or appaloosa
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13
Q

describe Ee (4)

A
  1. both black and red factoes detected
  2. can transmit either E or e to offspring
  3. base color of the horse is black, bay, or brown
  4. includes buckskin, zebra dun, grullo, perlino, gray, tobiano, overo, roan, or appaloosa
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14
Q

describe ee (3)

A
  1. only red factor detected
  2. base color is sorrel or chestnut (same thing = red)
  3. includes palomino, red dun, gray, cremello, tobiano, overo, roan, or appaloosa
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15
Q

describe the manes and tails of ee horses

A

manes and tails may be lighter (flaxen), or darker (BUT NOT BLACK), or could just be same color as the rest of the body

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16
Q

describe the confusing shit about chestnut and sorrel

A

they are the same color: red; just used in different areas;
AQHA says sorrel, byt thoroughbred people say chestnut

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17
Q

if you mate two ee horses, what color horse will you get?

A

only some shade of red because offspring will have to be ee

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18
Q

what is the longer name for gene A?

A

agouti signaling protein/agouti gene

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19
Q

what does gene A determine?

A

distribution of black pigmented hair

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20
Q

what does a dominant A in combination with dominant E yield?

A

will confine the black hair to the points to produce a BAY

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21
Q

describe the various shades of bay

A

range from dark bay (brown) through mahogany, blood, copper, and light bay

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22
Q

what are the 4 varations of the agouti gene? list in order of most to least dominant

A
  1. A+
  2. A
  3. At
  4. a
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23
Q

what must a horse have in its genotype in order to be a bay?

A

MUST have a dominant E and a dominant A

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24
Q

does the recessive agouti allele restrict the distribution of black hair? give what genotypes yield a uniformly black horse

A

no; because (aa) in the presence of the E allele produces a uniformly black horse
black: EE or Ee aa

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25
Q

describe A+ (3)

A
  1. wild bay
  2. black points of horse (legs) are not as extensive and appear washed out
  3. legs may have brown or silder appearing interspersed with black spots
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26
Q

describe A, give a personal example (2)

A
  1. traditional bay (Haida)
  2. black on legs extending to knee
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27
Q

describe At (3)

A
  1. dark brown (seal brown), but still genetically bay
  2. does not restrict black pigment as extensively as A+, but black is still washed out
  3. distinguished from black horse by brown hair around the muzzle and on flanks
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28
Q

what is the E and A genotype for a red horse? say why

A

ee_ _ (both _ could be A or a);
neither A nor a affects the pigment or its distribution in red (ee) horses, so it is not possible to tell by examination of coat color which alleles of the A gene a red horse has

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29
Q

describe A/A or A/a (3)

A
  1. black pigment distributed in a point pattern
  2. the horse will be BAY or BROWN in the ABSENCE of other modifying genes
  3. A has no effect on red pigment if (ee)
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30
Q

describe aa (3)

A
  1. only recessive allele is detected
  2. black pigment is distributed uniformly
  3. the horse will be BLACK in absence of other modifying genes
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31
Q

what are 2 modifications to base coat color?

A
  1. color dilutions to decrease the intensity of pigment
  2. white spotting or patterning
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32
Q

what is gene C? (2)

A
  1. cream gene
  2. pigment dilution
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33
Q

describe C^cr (2)

A
  1. incomplete dominance, affects color wothout a complete color change
  2. causes pigment dilution (of the red pigment)
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34
Q

what are fully pigmented horses’ genotypes for gene C?

A

CC (no dilution)

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35
Q

what happens to a bay (A_E_) when diluted with C^cr?; give

A

becomes a buckskin by dilution of the red body color to yellow WITHOUT affecting the black color of the mane and tail

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36
Q

give genetic formula for buckskin

A

A_E_CC^cr

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37
Q

what happens to a red horse (ee_ _) when diluted with gene C?

A

becomes a palomino through dilution of the red pigment in the body to yellow AND dilution of the mane and tail to flaxen/lighter

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38
Q

what is the genetic formula for a palomino horse?

A

ee _ _ CC^cr (could have any varation of AA Aa or aa because started from red horse)

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39
Q

can a genetically black horse (E_ aa) carry dilution?

A

yes, but not as noticeable

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40
Q

what does gene C^cr do in the homozygous condition? how do you get it? (3)

A
  1. completely dilutes coat color (double dilutes)
  2. results in very pale cream with white skin and blue eyes- cremello, perlino
  3. this is the product of mating two dilute-colored animals such as palominos or buckskins
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41
Q

what was a cremello before dilution?

A

was red (ee _ _)

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42
Q

what was a perlino before dilution?

A

was bay (E_ A_)

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43
Q

what was a smoky cream before dilution?

A

was black EE aa or Ee aa

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44
Q

describe CC (2)

A
  1. non-dilute
  2. basic colors are chestnut, bay, black, or brown in the absence of other color modifying genes`
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45
Q

describe CC^cr (4)

A
  1. heterozygous dilute
  2. chestnut diluted to palomino
  3. bay diluted to buckskin
  4. black diluted to smoky black
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46
Q

describe C^crC^cr (4)

A
  1. double dilute
  2. chestnut diluted to cremello
  3. bay diluted to perlino
  4. black diluted to smoky cream
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47
Q

what is gene D known for?

A

producing a dun patter and pigment dilution

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48
Q

is DD distinguishable from Dd?

A

nope

49
Q

what are 3 differences of the effects of gene D versus C^cr?

A
  1. D dilutes both red and black pigments on the BODY, but does not dilute either pigment on the points (C^cr dilutes only red pigment and can affect the points)
  2. gene D resuslts in the presence of a particular pattern which can include dark points, a dorsal stripe, a shoulder stripe, and/or leg barring
  3. homozygosity for gene D does not produce the extreme dilution to cream as C^cr does
50
Q

is gene D a dominant gene?

A

yes

51
Q

what does the presence of at least one dominant D gene do to a red body color? (3)

A

can dilute it to a pinky-red, yellowish-red, or yellow

52
Q

what does the presence of at least one dominant D gene do to a black body color?

A

dilutes it to mouse gray

53
Q

describe leg barring as observed with the D gene

A

zebra stripes on legs

54
Q

describe a red horse with the D allele, give genotype

A

the D allele results in a pinkish red horse with dark points, know as red dun or claybank dun; genotype is ee _ _ CC D_ (don’t know agouti or second D allele)

55
Q

describe a bay horse with the D allele, give genotype

A

the D allele results in a yellow or yellow-ish red horse with blackpoints known as dun or buckskin dun; genotype is E_ A_ CC D_

56
Q

describe a black horse with the D allele, give genotype

A

the D allele results in a mouse gray color with black points known as a mouse dun or grulla; genotype is E_ aa CC D_

57
Q

in what two genotypes of horses can the effects of D and C^cr be easily confused? can a horse have both D and C^cr? if so, how do you distinguish?

A

A_ E_; can have both; D is only found in a few breeds of horses; in the USA it is only found in some pony and stock horse (quarter horse) breeds

58
Q

give the letters of the silver dapple (taffy) gene

A

Z is dominant and silver
N is normal and recessive

59
Q

how is the silver gene different from D and C^cr?

A

it acts on black pigment only

60
Q

what happens to the black on the body in the presence of the silver gene? what happens to mane and tail?

A

the black on the body is diluted to a darm cream/light chocolate and the mane and tail are diluted or white

61
Q

give the genotypes and corresponding effects of the silver gene

A

ZZ: dilution to a greater effect
ZN: dilution
NN: normal; no dilution

62
Q

in what 3 breeds of horses is the silver gene found?

A
  1. rocky mountain horses
  2. icelandics
  3. morgans
63
Q

what is an example of pleiotropy with the silver gene?

A

this gene can dilute black pigment but can also reuslt in malformation in the eyes, with ZZ having more severe malformation

64
Q

does the silver gene affect red horses?

A

nope

65
Q

give the letters of the champagne gene

A

Ch is dominant and champagne
N is normal and nonchampagne

66
Q

describe a red horse (ee) with a champagne allele (Ch) (3)

A
  1. is difficult to distinguish from cream horses but
  2. Ch results in gold color with flaxen mane and tail
  3. these are called golden and ivory champagne horses
67
Q

describe a bay horse (E_ A_) with a Ch allele

A

becomes amber champagne

68
Q

describe a black horse (EE aa) with a Ch allele

A

classic champagne

69
Q

describe the skin of Ch horses

A

has a pink hue that becomes speckled with age (speckles on the eyes, muzzle, and under the tail)

70
Q

describe the eye color of a champagne horse

A

blue at birth, then changing to green or amber

71
Q

what are 5 breeds that commonly carry the champagne allele?

A
  1. quarter horse
  2. tennessee walking horse
  3. saddlebred
  4. missouri
  5. fox trotter
72
Q

describe the roan (Rn) gene (5)

A
  1. Rn is dominant
  2. mixture of individual white and colored hair in animals
  3. head and points will be colored hair
  4. non-progressive pattern: born with it and remains that same over the course of life
  5. amount of roan may vary with season as white and roan hairs grow differently
73
Q

describe the gray gene (G) (2)

A
  1. exclusion of pigment from hair
  2. progressive depigmentation, so hair gets more gray with age
74
Q

describe a horse with the gray allele at birth

A

will be born any color but gray and gradually become white or “flea-bitten” as an aged animal

75
Q

describe a “flea bitten” coat color

A

white with red or black flecks

76
Q

give the genotypes and corresponding phenotype of the gray allele

A

GG: gray
Gg: gray
gg: non-gray

77
Q

what is the earliest indication of a horse with the G allele changing to gray?

A

gray hairs seen around the eyes

78
Q

describe the intermediate stages of the graying process for horses with a (G) allele

A

horses will have a mixture of white and dark hairs (BUT NOT ROAN); two general patterns are dapple and flea-bitten

79
Q

how long does it take for a horse with the (G) allele to turn from color to gray?

A

6-8 years

80
Q

what is a bad thing often observed in gray horses? how common is it and what is the only good point?

A

high incidence of dermal melanomas around the tail and head; over 70% of grat horses older than 15 years will develop melanoma but they have lower malignancy

81
Q

even though they are less malignant, what is tricky about the dermal melanomas observed in over 70% of gray horses older than 15?

A

if in a tricky area like the jaw or the anus it can be an issue

82
Q

describe white patterning, generally (4)

A
  1. dominant white variants cause white markings but not necessaarily across the entire body
  2. some variants are lethal in the homozygous state
  3. there are more than 24 mutations associated with white markings
  4. horses will have pink skin! so watch for sun!!
83
Q

describe the tobiano white spotting pattern (3)

A
  1. variable restricted pattern of white hair with underlying pink skin which can occur with any coat color
  2. pattern is present at birth and stable throughout life
  3. looks like paint was poured on top of a solid-colored horse; white crosses topline! head usually a solid color
84
Q

give the genotypes and associated phenotypes with tobiano coat color

A

TT: tobiano
Tt: tobiano
tt: solid coat color

85
Q

what are the 2 types of paints?

A

tobiano and overo

86
Q

describe the distribution of white in a tobiano

A

white extends from the neck crest, withers, and croup in an apparent top-to-bottom distribution on the whole body

87
Q

describe the legs, head, and tail of a tobiano

A

legs are usually white, the head is usually dark except for face markings, and there is white in the tail

88
Q

what can a homozygous dominant tobiano (TT) sometimes look like?

A

might have color spots mixed in the white areas

89
Q

list the genotypes and corresponding phenotypes of overo

A

O is dominant so
OO: overo
ON: overo
NN: normal

90
Q

which is more common in the US: tobiano or overo?

A

tobiano is more common than overo

91
Q

describe the white areas of an overo (5)

A
  1. white areas usually display more ragged edges than tobiano
  2. white DOES NOT extend over topline in overo
  3. white is horizontally arranged with pattern on body
  4. white patches commonly appeaar in middle of sides and neck
  5. white may appear on belly
92
Q

describe the back and head of an overo

A

colored back, often called the frame because it “frames” the white; head usually marked excessively with white

93
Q

describe the eyes of overos

A

sometimes blue

94
Q

describe the legs of overo horses

A

will have at least one dark leg

95
Q

is OO a good genotype to have? why or why not?

A

NO!! OO is lethal white foal syndrome; comes from crossing two overo horses (25% chance) and causes aganglionosis of the GI tract, where the lower part/large intestine develops without proper innervation so the foal cannot defecate and will die painfully

96
Q

is sabino a particular gene?

A

no; can refer to a variety of white markings

97
Q

describe Sb1

A

a specific sabino mutation that results in irregular white markings diffuse throughout the body

98
Q

describe a horse with one copy of the Sb1 allele (3)

A
  1. horse will have 2 or mroe white legs
  2. will have white markings, often with irregular edges
  3. can cause roaning on legs and lower body
99
Q

describe what is commonly referred to as a sabino horse (3)

A
  1. have a blaze
  2. have white on the lower lip
  3. have body spots on the mid-section
100
Q

describe a horse with 2 copies of the Sb1 gene

A

primarily white

101
Q

describe the relationship between clydesdales and sabino coat color

A

cyldesdales are called sabinos but DO NOT have the Sb1 gene; likely carry some other sabino variant

102
Q

what genes cause the splash white coat color?

A

multiple alleles on two different loci:
SW1, SW3, SW5 and N (loci MITF)
SW2, SW4, and N (loci PAX3)
MITF and PAX3 are associated woth melanocytes so affect pigmentation

103
Q

describe the dominance of the splash white alleles

A

most variants are dominant over N

104
Q

describe the expressivity of the splash white alleles

A

variable expressivity, so one gene has a range of phenotypes

105
Q

describe the effects of the SW1 splash white gene

A

additive; so one copy has SOME effect on genotype and two copies have additional impact (even more white)

106
Q

describe splashed white horses, typically (5)

A
  1. white legs with body white ventrally
  2. head is extensively white (some exceptions)
  3. crisp edges between white and colored areas
  4. blue eyes are common
  5. sometimes resembles sabino
107
Q

how are splash white horses described?

A

as if horses were dipped in white paint

108
Q

what is the downside of the genotypes associated with splash white horses?

A

SW2, SW3, SW4, and SW4(SW5) may be homozygous lethal

109
Q

in what breeds is the splash white coat color usually found? (4)

A
  1. quarter horses
  2. icelandic
  3. paint
  4. trakehner
110
Q

what alleles are associated with appaloosa coat color?

A

Lp and PATN1

111
Q

describe the Lp gene

A

also called leopard complex spotting locus; leads to a white coat pattern characterized by variable patterning with or without pigmented spots known as leopard spots (determines the presence of appaloosa pattern)

112
Q

describe the PATN1 gene

A

modifier of Lp in appaloosas; controls the amount of white in the coat, increasing the amount of white present in horses that also have the Lp mutation (determines what the appaloosa pattern looks like)

113
Q

describe the leopard complex associated with appaloosas (4) what are these horses also called as they age?

A
  1. mottled skin
  2. striped hooves
  3. white sclera
  4. progressive loss of pigment in the coat (called roaning but NOT ROAN) with age
    also called varnish roan once this loss of pigment begins
114
Q

describe a horse that is homozygous for leopard complex (LP/LP)

A

minimal to extensive white pattern with few to no pigemented spots; size of the pattern is dependent on the modifiers present

115
Q

what are 2 downsides observed in horses homozygous for the leopard complex (LP/LP)?

A
  1. congenital stationary night blindness (CSNB)
  2. elevated risk for equine recurrent uveitis (ERU)
116
Q

describe a horse with the LP/N genotype

A

variable white pattern with pigmented spots; size of white pattern depends on what patterning modifiers are also present

117
Q

describe PATN1 (4)

A
  1. appaloosa pattern-1
  2. modifers of LP
  3. controls the amount of white in the coat
  4. increasing the amount of white present in horses that also have LP mutation
118
Q

describe N/PATN1 horses that are also LP (N/LP or LP/LP)

A

will have high amounts of white patterning; typically more than 60% at birth

119
Q

describe PATN1/PATN1 horses that also have at least one copy of LP

A

have high amounts of white patterning (almost white looking)

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