Transcript Incomplete & Codominance Powerpoint

Incomplete & Codominance
Genetics
Biology 30
Mrs. 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
W
http://www.usask.ca/biology/genetics/extensions/
snapdragon.jpg
W
Genotype: All Ww
w
Ww
Ww
Phenotype: All Pink
w
Ww
Ww
F1 x F1 Cross
http://www.visionle
arning.com/library/
modules/mid129/Im
age/VLObject3228050216120240.jpg
Ww X Ww
W
w
W
WW
Ww
w
Ww
ww
Remember:
W = red w = white Ww = pink
Genotypic Ratio:
1WW: 2 Ww: 1ww
Phenotypic ratio:
1 Red: 2 Pink: 1 White
***NOTE: Because there is no dominance in the heterozygote the
phenotypic ratio is identical to the genotypic ratio****
•
http://courses.bio.psu.edu/fall2
005/biol110/tutorials/tutorial5_f
iles/figure_14_9.gif
http://library.thinkquest.org/2046
5/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
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).
Blue Roan Example:
http://www.virginiacowboy.com/sitebuilder/images
/DSC_0040-803x536.jpg
Red Roan Example:
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
L ML M = 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
LM
 Phenotypic Ratio:
1 M blood type: 1 MN blood type
LM
LM
LMLM
LMLM
LN
LMLN
LMLN
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