What color was this horse at birth

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What color was this horse at birth?
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Fox photos provided by Sarah Pinkney
Tie
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Spot
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Snip
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Silver
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Platinum
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Platinum
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Narvikpup
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Mix
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Georgian
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Georgian
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Silverdad
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Lecture 6
Epistasis
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Two-Loci Ratios
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AaBb AaBb (autosomal dominant)
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AaBb AaBb (autosomal dominant)
3 A_ 1 aa 3 B- 1 bb 9 A_B_ 3 A_bb 3 aaB_ 1
aabb
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AaBb AaBb (autosomal dominant)
3 A_ 1 aa 3 B- 1 bb 9 A_B_ 3 A_bb 3 aaB_ 1
aabb

• Independent
• Dominance
• No lethal
• Autosomal
• Two allele/ locus

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Types of Two-Loci Interaction
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Epistasis

• Interaction of genes at different loci.

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Epistasis

• Interaction of genes at different loci.
• Masking -- gene or genotype at one locus masks
  the expression of genotypes at a second locus.

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Epistasis

• Interaction of genes at different loci.
• Masking -- gene or genotype at one locus masks
  the expression of genotypes at a second locus.
• Modifying -- same as above but modifies
  expression rather than masks.

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Masking Epistasis (recessive)
Example -- coat color in Labs
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Masking Epistasis (recessive)
Example -- coat color in Labs
B_ black bb brown E_ allows expression of B
locus ee yellow regardless of B locus
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Masking Epistasis (recessive)
Example -- coat color in Labs
B_E_ black bbE_ brown _ _ee yellow
Therefore,
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Yellow Labs
B_ee yellow with black nose bbee yellow
with pale nose and lips Willis Genetics of
the Dog, 1989
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Inter se mating of F1s
BbEe BbEe
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Inter se mating of F1s
BbEe BbEe
9 B_E_ black 3 B_ee yellow 3 bbE_ brown 1
bbee yellow
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Inter se mating of F1s
BbEe BbEe
9 B_E_ black 3 B_ee yellow 3 bbE_ brown 1
bbee yellow
--9 black to 3 brown to 4 yellow--
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Masking Epistasis (dominant)
Example -- Gray in horses
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Masking Epistasis (dominant)
Example -- Gray in horses
G_ Gray at maturity gg Not Gray E_ Black
ee Chestnut
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Inter se mating F1s
GgEe GgEe
9 G_E_ 3 G_ee 3 ggE_ 1 ggee
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Inter se mating F1s
GgEe GgEe
9 G_E_ 3 G_ee 3 ggE_ 1 ggee
12 G_ _ _
3 ggE_ 1 ggee
Correction
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Inter se mating F1s
GgEe GgEe
At maturity 12 G_ _ _ 12 Gray
9 G_E_ 3 G_ee 3 ggE_ 1 ggee
3 ggE_ 3 Black 1 ggee 1
Chestnut
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Modifying Epistasis
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Modifying Epistasis
Modifying epistasis a gene or genotype at one
locus modifies the expression of genotypes at a
second locus.
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Modifying Epistasis
Example -- coat color in Dobermans
B_ black bb red D_ full expression of B
locus dd dilution of color at B locus
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Modifying Epistasis
Example -- coat color in Dobermans
Therefore,
B_D_ black bbD_ red B_dd blue
(faded black) bbdd fawn (faded red)
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Inter se mating of F1s
BbDd BbDd
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Inter se mating of F1s
BbDd BbDd
9 B_D_ black 3 B_dd blue 3 bbD_ red 1
bbdd fawn
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Identical Phenotypes
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Identical Phenotypes
Gene or genotype at one locus producing an
identical phenotype to that produced by a gene or
genotype at a second locus.
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Identical Phenotypes
9 A_B_
Combine based on phenotypes
3 A_bb
3 aaB_
1 aabb
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9 A_B_
Combine based on phenotypes
3 A_bb
3 aaB_
1 aabb
Locus 1 Locus 2 Ratio
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9 A_B_
Combine based on phenotypes
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3 A_bb
3 aaB_
1 aabb
Locus 1 Locus 2 Ratio dominant A
dominant B 15 to 1
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9 A_B_
Combine based on phenotypes
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3 A_bb
1 aabb
3 aaB_
Locus 1 Locus 2 Ratio dominant A
dominant B 15 to 1 dominant A recessive
bb 13 to 3
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9 A_B_
Combine based on phenotypes
3 A_bb
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3 aaB_
1 aabb
Locus 1 Locus 2 Ratio dominant A
dominant B 15 to 1 dominant A recessive
bb 13 to 3 recessive aa recessive bb
9 to 7
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Dominant / Dominant
Example -- Spotted horses
T gt t Tobiano O gt o Overo
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TtOo TtOo
9 T_O_ Spotted 3 T_oo Spotted 3
ttO_ Spotted 1 ttoo solid
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TtOo TtOo
9 T_O_ Spotted 3 T_oo Spotted 15 3
ttO_ Spotted 1 ttoo solid 1
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TtOo TtOo
9 T_O_ Spotted 3 T_oo Spotted 15 3
ttO_ Spotted 1 ttoo solid 1
Caution OO may be lethal
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Dominant/ Recessive
Example -- white in chickens
W_ white ww color I_ color ii
white
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WWII wwii
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WWII wwii
WwIi
F1 generation
white
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WWII wwii
WwIi
F1 generation
white
9 W_I_ white 3 W_ii white 3 wwI_ color 1
wwii white
F2 generation
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WWII wwii
WwIi
F1 generation
white
9 W_I_ white 3 W_ii white 3 wwI_ color 1
wwii white
F2 generation
13 white to 3 color
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Recessive/ Recessive
Example -- pastel mink
B_ natural dark bb pastel G_ natural
dark gg pastel
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bbGG BBgg
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bbGG BBgg
BbGg
F1 generation
natural dark
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bbGG BBgg
BbGg
F1 generation
natural dark
The appearance of the dominant phenotype, natural
dark, from the mating of recessive strains is the
classic clue that there are two recessive
genotypes mimicking each other.
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bbGG BBgg
BbGg
F1 generation
natural dark
9 B_G_ natural dark 3B_gg pastel 3
bbG_ pastel 1 bbgg pastel
F2 generation
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bbGG BBgg
BbGg
F1 generation
natural dark
9 B_G_ natural dark 3B_gg pastel 3
bbG_ pastel 1 bbgg pastel
F2 generation
9 natural dark to 7 pastel
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Harlequin
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Harlequin
Phenotype appears in dogs that are Hh at the
locus for harlequin. but are also Mm at the
merle locus.
Harlequin is not observed in dogs that are either
HhMM or Hhmm.
HH is lethal.
Sponenberg, D.P., 1985, Journal of Heredity, page
224
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Genotypes
Relationship of phenotypes to genotypes
Genotype Phenotype MMh- Mostly white
(pale) MmHh Harlequin Mmhh Merle
mmh- Non-merle
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2 Hh 1 hh
1MM 2Mm 1 mm
3 _hMM White 4 HhMm Harlequin 2 hhMm
Merle 3 mmh_ nonmerle
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Codominance at A Dominance at B
1 AA 2 Aa 1 aa
3 B_ 1 bb
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Codominance at A Dominance at B
1 AA 2 Aa 1 aa
3 B_ 1 bb
3 AAB_ 1 AAbb 6 AaB_ 2 Aabb 3 aaB_ 1
aabb
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Lethal at A Dominance at B
2 Aa 1 aa
3 B_ 1 bb
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Lethal at A Dominance at B
2 Aa 1 aa
3 B_ 1 bb
6 AaB_ 3 aaB_ 2 Aabb 1 aabb
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Lethal at Both
2 Aa 1 aa
2 Bb 1 bb
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Lethal at Both
2 Aa 1 aa
2 Bb 1 bb
4 AaBb 2 aaBb 2 Aabb 1 aabb