Incomplete and Codominance

Target

SWBAT determine if a trait shows complete, incomplete or codominance.

Review: Complete/Classic Dominance

When dominant alleles overpower the recessive allele.One dominant is all that is needed for an individual to show the dominant phenotype.

Example: Complete/Classic Dominance

Ex: Eye Color (B=Brown, b=Blue)

BB and Bb = Brownbb= blue

Incomplete DominanceWhen two or more alleles influence the phenotype.No allele is completely dominant, therefore, heterozygous individuals will show an intermediate (or third) phenotype.

Incomplete Dominance Example

Four o’clock Flowers Alleles:

R = Redr = White

RR

Red Flowers

rr

White Flowers

RrIntermediate Phenotype =

Pink

Codominance

Both alleles are equally dominant.Both alleles are therefore expressed equally in the phenotype of heterozygous individuals.

Codominance Example

Horse Coat ColorAlleles:

R = Redr = White

RR

Red Coat Color

rrWhite Coat Color

RrRoan Coat

Color (Red and

White hairs)

Other Codominant Traits

Practice Problems

Assuming incomplete dominance... If: R = Red and r = blueWhat phenotypes would you see

with:–RR=–rr =–Rr =

Assuming incomplete dominance... If: R = Red and r = blueWhat phenotypes would you see

with:–RR= Red– rr = Blue–Rr = Purple

Practice Problem

Assuming codominance... If: R = Red and r = blueWhat phenotypes would you see

with:–RR=–rr =–Rr =

Assuming codominance... If: R = Red and r = blueWhat phenotypes would you see

with:–RR= Red– rr = Blue–Rr = Red and Blue (Spots, Stripes, etc)

Dominance Combinations

Sometimes certain alleles are completely dominant and others are not.This is the case with blood types

Blood Types

Blood Type alleles–A: Completely dominant to o; codominant with B

–B: Completely dominante to o; codominant with A

–o: Completely recessive

Blood Types

Genotype

AA

Ao

BB

Bo

AB

oo

Phenotype

A blood type

A blood type

B blood type

B blood type

AB blood type

O blood type

Interesting Blood Donating Facts

O has no A or B antibodies and can be given to anyone.AB individuals have both types of antibodies and can take any kind of blood.