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Incomplete & Codominance. 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. - PowerPoint PPT Presentation
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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
CR = red CW = white
Parents are both true breeding red and white.
Parents: Red X White
CRCR X CWCW
Genotype: All CRCW
Phenotype: All Pink
CR CR
CW CRCW CRCW
CW CRCW CRCW
http://www.usask.ca/biology/genetics/extensions/snapdragon.jpg
F1 x F1 Cross
CRCW X CRCW
Remember: CR = red CW = white
Genotypic Ratio:
1 CRCR : 2 CRCW : 1 CWCW
Phenotypic ratio:
1 Red: 2 Pink: 1 White
CR CW
CR CRCR CRCW
CW CRCW CWCW
***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 . . .
• CRCR = have enough pigment to be red.
• CWCW = flowers don’t have any pigment.= no color
• CRCW = 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).
Red Roan Example: http://www.naturalselectionreptiles.com/Genetics/exCodominance.jpg
Blue Roan Example: http://www.virginiacowboy.com/sitebuilder/images/DSC_0040-803x536.jpg
Red Roan Example:http://www.brokenlfarm.com/images/sale/kbrowdypetejr/102_8424.JPG
Coat Color in Horses• C= Color gene• CRCR = Red • CWCW = White • CRCW = Red Roan If you cross a true breeding Red horse with a true breeding white
horse, what ratios will you get?
Genotypic Ratio:
All CRCW
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
• O (ii) is recessive to IA and IB.• Genotypes IAIA and IAi result in Type A phenotype.• Genotypes IBIB and IBi result in Type B phenotype.• Genotype IAIB results in Type AB phenotype (codominant).• Genotype ii results in Type O phenotype.
• Surface proteins are like nametags and antibodies clump up foreign blood
• Useful in blood transfusion and organ transplant
Resource Sites• Incomplete & Codominance Explained:
– http://www.hobart.k12.in.us/jkousen/Biology/inccodom.htm• Codominance - Incomplete Dominance (Brightstorm Video)
– http://www.brightstorm.com/science/biology/mendelian-genetics/codominance-incomplete-dominance/
• Practice: Drag and Drop Pedigrees– http://www.zerobio.com/drag_gr11/pedigree/pedigree4.htm
• More Practice from KSU:– http://www.ksu.edu/biology/pob/genetics/incom.htm