Notes: Incomplete/Codominance (page 12)

Notes: Incomplete/Codominance (page 12)

• So far, we have learned about simple Mendelian inheritance--traits controlled by dominant and recessive paired alleles

Notes: Incomplete/Codominance (page 12)

• So far, we have learned about simple Mendelian inheritance--traits controlled by dominant and recessive paired alleles

• However, MOST alleles are not simply dominant or recessive

• Incomplete Dominance = The phenotype of the heterozygote is intermediate between those of the two homozygotes

Example: Snapdragons

• RR = Red

Example: Snapdragons

• RR = Red

• WW= White

Example: Snapdragons

• RR = Red

• WW= White

• RW = Pink

Example: Hair

• CC = Curly SS = Straight CS= Wavy

Example: Hair• CC = Curly SS = Straight CS= Wavy• Punnett square problem: 2 Wavy haired

people have a child

C S

C

S

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

CC CS

CS SS

Practice Problem: Incomplete Dominance (pg 13)

• 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

(pg 12)

• Codominance = the heterozygote produces the phenotypes of BOTH homozygotes

Example: Chickens

• BB = Black• WW = White

Example: Chickens

• BB = Black• WW = White• BW = Checkered

Other examplesCows: RR = RedWW= White RW=Roan (red and white spots)

Horses: GG = Gray WW = WhiteGW=Apaloosa (white with gray spots)

• Punnett square problem: 2 appaloosa horses are crossed

G W

G

W

• Punnett square problem: 2 appaloosa horses are crossed

G W

G 25% Gray

W 50% Appaloosa 25% White

GG GW

GW WW

Codominance Practice Problem (pg 13)

• For each practice problem, draw the Punnett square and give the phenotype ratios

A. Cross a checkered chicken with a black chicken

B. Cross two checkered chickens together

Output Activity (pg 13)

• 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.