Incomplete & CodominanceIncomplete & Codominance
Genetics Genetics
Biology 30Biology 30
Mrs. S. Pipke-PainchaudMrs. S. Pipke-Painchaud
Reviewing
All photos from: http://www.naturalselectionreptiles.com/Genetics.html
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 O’Clocks or Morning Glory or Primrose (Flowers)
– Curly (homozygous) or straight (homozygous), but if you are heterozygous you have wavy hair.
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
W W
w Ww Ww
w Ww Ww
http://www.usask.ca/biology/genetics/extensions/snapdragon.jpg
F1 x F1 Cross
Ww X WwRemember:
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****
http://www.visionlearning.com/library/modules/mid129/Image/VLObject-3228-050216120240.jpg
• http://courses.bio.psu.edu/fall2005/biol110/tutorials/tutorial5_files/figure_14_9.gif
http://library.thinkquest.org/20465/media/flowers.gif
How the coloring works . . .
• WW – have enough pigment to be red
• ww - flowers don’t have any pigment = no color
• Ww – only have enough pigment to be pink
CodominanceCodominance
• 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).
Red Roan Example: http://www.naturalselectionreptiles.com/Genetics/exCodominance.jpg
Blue Roan Example: http://www.virginiacowboy.com/sitebuilder/images/DSC_0040-803x536.jpg
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
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
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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