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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 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