Color blocking factor
Alleles
W (white) or w (not white)
WW or Ww: Homozygous WW is considered a lethal gene; Ww will result in white horses
Expressed
ww: Most horses are ww as truly white horses are very rare
Not Expressed
Gray Factor
G (gray) or g (not gray)
Allele
Expressed
GG or Gg: turns gray with age
gg: does not turn gray with age
Not Expressed
Extension Factor
E (black) or e (red)
Allele
EE or Ee: Able to form black pigment in skin and hair (points or all over)
Expressed
ee: black pigment in skin but blocked from hair, therefore hair appears red
Not Expressed
Agouti factor
A (bay) or a (black)
Allele
AA or Aa: causes black pigment to be restricted to points; has no effect on red pigment
Expressed
aa: if horse has black hair, uniformly distributed over body and points; has no effect on red (ee) pigment
Not Expressed
Dun Dillution Factor
D (dun) or d (not dun)
Allele
DD or Dd: shows diluted body color and has dark points; dorsal stripe and shoulder stripe and leg barring
Expressed
dd: undiluted coat color; Not dun
Not Expressed
Cream Dilution Factor
C (full color), Cr (cream)
Allele
CCr: Red pigment diluted to yellow; black unaffected
CrCr: Both red and black pigments are diluted; skin and eye color diluted
Expressed
CC: fully pigmented; no cream dilution
Not Expressed
Roan Factor
Allele
RN (roan) or rn (not roan)
RNRN or RNrn: causes white hairs to be mixed with base coat color; does not progress as in gray (G) factor
Expressed
rnrn: No roaning effect
Not Expressed