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Notes: Incomplete/ Codominance

Notes: Incomplete/ Codominance. MOST alleles are not simply dominant or recessive Rr  not always the correct model! RW?? WTF???. Incomplete Dominance = The phenotype of the heterozygote is intermediate between those of the two homozygotes Mixed or blended like paints.

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Notes: Incomplete/ Codominance

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  1. Notes: Incomplete/Codominance

  2. MOST alleles are not simply dominant or recessive • Rr not always the correct model! • RW?? • WTF???

  3. Incomplete Dominance = The phenotype of the heterozygote is intermediate between those of the two homozygotes • Mixed or blended like paints

  4. Remember, alleles code for protein production. • In incomplete dominance, the dominant gene does not code for all of the protein, the “recessive” gene codes also. • The result = a mix/blend of phenotype

  5. Example: Snapdragons • RR = Red

  6. Example: Snapdragons • RR = Red • WW= White

  7. Example: Snapdragons • RR = Red • WW= White • RW = Pink

  8. Example: Hair • CC = Curly • SS = Straight • CS= Wavy

  9. Example: Hair • CC = Curly SS = Straight CS= Wavy • Punnett square problem: 2 Wavy haired people have a child C S C S

  10. Example: Hair • CC = Curly SS = Straight CS= Wavy • Punnett square problem: 2 Wavy haired people marry C S C 25% Curly S 50% Wavy 25% Straight

  11. Practice Problem: Incomplete Dominance (pg 12) • For each practice problem, draw the Punnett square and give the phenotype ratios A: Cross a pink snapdragon with a white snapdragon B: Cross a red snapdragon with a white snapdragon

  12. Codominance = the heterozygote produces the phenotypes of BOTH homozygotes (no mixing or intermediate)

  13. Example: Chickens • BB = Black • WW = White

  14. Example: Chickens • BB = Black • WW = White • BW = Checkered

  15. Other examples Cows: RR = Red WW= White RW=Roan (red and white spots) Horses: GG = Gray WW = White GW=Apaloosa (white with gray spots)

  16. Punnett square problem: 2 appaloosa horses are crossed G W G W

  17. Punnett square problem: 2 appaloosa horses are crossed G W G 25% Gray W 50% Appaloosa 25% White

  18. Codominance Practice Problem (pg 12) • For each practice problem, draw the Punnett square and give the phenotype ratios • Cross a checkered chicken with a black chicken • Cross two checkered chickens together

  19. Output Activity • Make up an incomplete/codominance problem that requires a Punnett square to solve. You must make up a NEW trait, and explain the phenotypes of the homozygotes and the heterozygotes in the problem.

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