INCOMPLETE DOMINANCE

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CHAPTER 11.3
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CHAPTER 11.3

• INCOMPLETE DOMINANCE
• When the hybrid is a new in-between phenotype
  of the two pure breeds
• Example P red flowers X white flowers
• F1 pink flowers
• Black X white ? Gray
• Blue X yellow ? green

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CHAPTER 11.3

• RR red WW white RW pink

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CHAPTER 11.3

• Pink X pink RW X RW
• ¼ red
• ½ pink
• ¼ white

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CHAPTER 11.3

• You will always be told if a trait shows
  incomplete dominance otherwise consider it the
  normal dominance and recessive patterns.

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CHAPTER 11.3

• Co-dominance
• When both allele forms in a hybrid are seen
• Example roan coat color
• Brown fur X white fur ? roan (both white and
  brown hairs are present side by side)

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CHAPTER 11.3
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CHAPTER 11.3

• Erminette chickens the gene for feather color
  has two codominant alleles one for black
• feathers and one for
• white feathers
• written the same way
• that incomplete
• dominance is written

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CHAPTER 11.3

• You will always be told if a trait shows
  codominance otherwise consider it the normal
  dominance and recessive patterns.

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CHAPTER 11.3

• Multiple alleles
• When there are more than just two allele forms
  possible for the same gene pair
• Trait is still controlled by just one gene pair
  there are just more possibilities

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CHAPTER 11.3

• examples of multiple alleles
• Coat color in rabbits
• Determined by a single gene pair that has four
  alleles

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CHAPTER 11.3

• Human blood group
• Three alleles two dominant over another but not
  each other
• Type A AA, AO
• Type B BB, BO
• Type AB - AB
• Type O OO
• Typically use the letter I or i (representing
  immunoglobulin) and superscript of A or B

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CHAPTER 11.3

• Polygenic traits
• When one trait is controlled by several gene
  pairs
• The combination taken all together creates the
  phenotype
• Examples human skin color feather color in
  parakeets

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P GENERATION
aabbcc(very light)
AABBCC(very dark)
F1 GENERATION
AaBbCc
AaBbCc
Eggs
Sperm
Fraction of population
Skin pigmentation
F2 GENERATION
Figure 9.16
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CHAPTER 11.3

• Parakeet feather colors
• Green
• BBYY
• BBYy
• BbYY
• BbYy
• Blue
• BByy
• Bbyy
• Yellow
• bbYY
• bbYy
• White
• bbyy

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CHAPTER 11.3

• Cross a blue parakeet (Bbyy) with a yellow
  parakeet (bbYy).

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CHAPTER 11.3

• Bbyy X bbYy

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CHAPTER 11.3

• What are the possibilities of a white parakeet
  from this mating?
• ½ bb X ½ yy ¼ bbyy