HORSE COLOR GENETICS

Equine ScienceMr. Dieckhoff

BASIC GENETICS

Heredity Process of passing traits on to offspring

Genes The basic unit of inheritance A DNA sequence at a specific location on a

chromosome, occur in pairs

CHROMOSOMES

Human – 23 pairs (46 total) Chicken – 39 pairs (78 total) Cattle – 30 pairs (60 total) Sheep – 27 pairs (54 total) Swine – 19 pairs (38 total) Horse – 32 pairs (64 total) Donkey – 31 pairs (62 total) Mule – 63 total

TERMINOLOGY

Locus Region of chromosome where particular

gene is carried Allele

Alternative forms of gene at locus Genotype

Pair of alleles at given locus Actual genetic makeup of individual

TERMINOLOGY

Homozygous Same alleles at both loci

Heterozygous Different alleles at both loci

Phenotype Expression of alleles, what they look like

MODES OF GENE ACTION

Complete Dominance One allele “masks” expression of another Ex: black coat color in angus cattle

BB = Black; bb = Red; Bb = Black

Partial or Incomplete Dominance One allele does not completely “mask”

expression of another allele Ex: coat color in Shorthorn cattle

RR = Red; rr = White; Rr = Roan

PUNNETT’S SQUARE

If two roan shorthorns are bred, what are expected genotypes and phenotypes of their progeny?

QUALITATIVE COAT COLOR

More than 10 loci involved At any one locus, effects are generally

due to dominance Two types of skin pigmentation

Eumelanin (black or brown) Pheomelanin (red or yellow)

GENE W : WHITE

Can mask all other genes W dominant to w

WW : lethal Ww : true white

Pink skin and white hair ww: not white

Color depends on other genes

GENE G : GRAY

G dominant to g G_: gray

All gray horses must have one gray parent Flea-bitten grays are probably Gg

gg: not gray

GENE E : EUMELANIN (BLACK HAIR)

E dominant to e E_: black hair (whole body or points)

Black, brown, bay, buckskin, etc. ee: red hair

Sorrel, chestnut, palomino, etc.

GENE A : AGOUTI (BLACK POINTS)

Controls distribution of black hair (E_) E_A_

Black points; bay E_aa

Black body, black, brown Ee aa / ee A_

Chestnut, sorrel

GENE C : CREAM DILUTION

Controls dilution of red pigment CC: full pigment CCcr: yellow body

Bay = buckskin (E_A_CCcr) Sorrel = palomino (ee CCcr) Black = smoky black (E_aaCCcr)

GENE C : CREAM DILUTION

Controls dilution of red pigment CcrCcr dilutes any coat color

Pale cream with pink skin and blue eyes

GENE C : CREAM DILUTION

Cremello (ee CcrCcr) Will always produce buckskins, palominos,

or smoky blacks Perlino (E_A_CcrCcr)

Will always produce buckskins, palominos, or smoky blacks

Smoky Cream (E_aaCcrCcr)

GENE D : DUN GENE

Dilutes both black and red coat color, but not dark points

Characteristics Darker points Dorsal stripe Shoulder stripe Leg barrrings

D dominant to d

GENE D : DUN DILUTION

Black base coat E_aaCCdd : black E_aaCCD_: grulla / grullo

Bay base coat E_A_CCdd: bay E_A_CCD_: bay dun or buckskin dun

Chestnut base coat eeCCdd: chestnut eeCCD_: red dun

GENE Rn: ROAN

Rn is dominant to rn Rn__: roan rn rn: non roan

Must have at least one roan parent

GENE Ch : CHAMPAGNE DILUTION

Dominant Gene Must have at least one Champagne

parent Controls dilution of hair from black to

brown and red to gold Skin is lavender and speckles with age Eye are amber

GENE Ch : CHAMPAGNE DILUTION

Chestnut base coat eeNN: chestnut eeCh_: “gold” often with flaxen mane & tail

Bay base coat E_A_NN: bay E_A_Ch_: “amber”; tan with black points

Black base coat E_aaNN: black E_aaCh_: “classic”; darker tan with brown

points

GENE Z : SILVER DILUTION

Dominant gene Must have one silver parent Controls dilution of black pigment

NN: full pigment NZ or ZZ:

Sorrel: no effect Bay: lightened pigment on lower legs and

flaxen mane and tail Black: chocolate with flaxen mane and tail

GENE Prl : PEARL DILUTION

Formerly “Barlink Dilution” Recessive gene Only seen in chestnuts Can interact with Cream Chestnut base coat

eeNN or NPrl: chestnut eePrlPrl: pale apricot color of body, mane,

and tail

COLOR CALCULATOR

http://www.animalgenetics.us/CCalculator1.asp

http://www.vgl.ucdavis.edu/services/coatcolor.php

APPLICATION (21 POINTS, 3 PTS EA)

Determine the color patterns of the following horses:

1. ww gg ee aa CC dd rnrn NPrl2. Ww Gg Ee aa CCcr dd rnrn NN3. ww gg Ee Aa CC dd rnrn NN4. ww gg Ee aa CC Dd rnrn NN 5. ww gg EE AA CC dd rnrn ZZ6. ww gg ee aa CcrCcr dd rnrn NN7. ww gg ee aa CC Dd RnRn NN

ANSWERS (21 POINTS, 3 PTS EA)

1. Chestnut or sorrel2. White3. Bay4. Gurlla / Grullo5. Chocolate with flaxen mane & tail6. Palomino or Cremello7. Red Roan Dun

QUIZ (9 POINTS)

1. ww gg ee aa CcrCcr dd rnrn NN

2. ww Gg Ea CC Dd Rnrn ZZ

3. ww gg ee aa CC Dd rnrn PrlPrl

ANSWERS

1. Buckskin, Palomino, or Smokey Black2. Flea Bitten Gray3. Chestnut with apricot body, mane, tail