Incomplete

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Incomplete Codominance

• Genetics
• Biology 30
• Mrs. S. Pipke-Painchaud

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Reviewing
All photos from http//www.naturalselectionrepti
les.com/Genetics.html
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Incomplete Dominance

• (a.k.a. partial dominance or blending) 
• occurs when both alleles contribute to a trait
  that is not like either parent. 
• this condition is only seen in the heterozygous
  individual 
• ex.. Snap Dragons or Four OClocks or Morning
  Glory or Primrose (Flowers)
• Curly (homozygous) or straight (homozygous), but
  if you are heterozygous you have wavy hair.

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Example Snap Dragons

• Parents Red  X  White 
• W red  w   white 
• ? Parents are both true breeding red and white.
• WW  X ww 
• Genotype All Ww
• Phenotype All Pink

http//www.usask.ca/biology/genetics/extensions/sn
apdragon.jpg
W W
w Ww Ww
w Ww Ww
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F1 x F1 Cross
http//www.visionlearning.com/library/modules/mid1
29/Image/VLObject-3228-050216120240.jpg

• Ww X Ww
• Remember
• W red  w   white Ww pink
• Genotypic Ratio
• 1WW 2 Ww 1ww
• Phenotypic ratio
• 1 Red 2 Pink 1 White

W w
W WW Ww
w Ww ww
NOTE  Because there is no dominance in the
heterozygote the phenotypic ratio is identical to
the genotypic ratio 
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• http//courses.bio.psu.edu/fall2005/biol110/tutori
  als/tutorial5_files/figure_14_9.gif

http//library.thinkquest.org/20465/media/flowers.
gif
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How the coloring works . . .

• WW have enough pigment to be red
• ww  -  flowers dont have any pigment no
  color
• Ww only have enough pigment to be pink

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Codominance

• the two dominant genes are expressed at the same
  time 
• both traits appear in the heterozygous
  individual at the same time
• ex.. Roan (Red or Blue) coat color in horses and
  cattle 
• Chestnut and White color in horses are both
  dominant traits the heterozygous individual is a
  palomino (golden).

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Blue Roan Example http//www.virginiacowboy.com/s
itebuilder/images/DSC_0040-803x536.jpg
Red Roan Example http//www.naturalselectionrepti
les.com/Genetics/exCodominance.jpg
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Coat Color in Horses

• C Color gene
• CR CR  Red CW CW White
• CR CW Red Roan
• If you cross a true breeding Red horse with a
  true breeding white horse, what ratios will you
  get?
• Genotypic Ratio
• All CR CW
• Phenotypic Ratio
• All Red Roan

CR CR
CW CR CW CR CW
CW CR CW CR CW
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Example MN Blood Group

• MN blood group is characterized by a certain
  type of glycoprotein on the surface of the
  RBCs. 
• There are two forms M and N
• Designate is L
• LMLM  M
• LNLN N
• LMLN  MN type 

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MN Blood Group

• LMLM  M
• LNLN N
• LMLN  MN type 
• What types of offspring would be produced from a
  cross of a homozygous M type with an MN type?
• Parents LMLM X LMLN
• Genotypic Ratio
• 1 LMLM 1 LMLN
• Phenotypic Ratio
• 1 M blood type 1 MN blood type

LM LM
LM LMLM LMLM
LN LMLN LMLN
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Resource Sites