Codominance
With codominance neither allele is dominant, they both show up in the offspring
Lets look at flower color
In codominance a plant with red flowers mating with one having white flowers produces a plant with both red & white flowers
Again we write the alleles differently Lower case designation indicates Codominance
For flower color:
Cr Cr Red Flowers
Cw Cw = White Flowers
Cr Cw = Red & White Flowers
Codominance
Lets cross a homozygous red plant with a heterozygous one
What are the chances of our baby plant having red & white flowers?
Review...
Let's cross flowers... What will we get?
1­ Give the phenotypes for the parents
2­ Give the phenotypes and genotypes for the offspring.
3­ Identify each as complete, incomplete, or codominance.
w w r w C C X C C
Rr x Rr
W W X CR CW
C C
w w r w C C X C C
Rr x Rr
CW CW X CR CW
Answers
w w r w C C X C C
1­ red/white x white
Cw
Cr
C
w
Cr C
w
Cw Cw
C
w
Cr C
w
Cw Cw
2­ Genotypes:
50 % Cr Cw 50% Cw Cw
Phenotypes:
50% red/white
50% white
3­ codominance
Rr x Rr
1­ red x red
R
r
W W X CR CW
C C
1­ white x pink
CR
W
C
R RR Rr
W
C CWCR CW W
C
r Rr
W
W
C CWCR C CW
rr
2­ Genotypes:
25% RR
50% Rr
25% rr
Phenotypes:
75% Red
25% White
3­ complete
dominance
2­ Genotypes:
50 % CW CR 50% CW CW
Phenotypes:
50% pink
50% white
3­ incomplete
dominance
Multiple Alleles
Some traits are controlled by multiple alleles
It still only takes two alleles to make a gene
However there are more than two options for alleles
For example, the eye color of fruit flies have four options for alleles
1
E = Red
2
E = Apricot
3
E = Honey
4
E = White
Multiple Alleles
Each allele is dominant to the remaining
1
E = Red
2
E = Apricot
3
E = Honey
4
E = White
E1 is dominant to E2, E3, & E4
E2 is dominant to E3 & E4
E3 is dominant to E4
E4 is the recessive allele
Options for genes would be:
1 4
E E = Red Eyes
2 3
E E = Apricot
4 4
E E = White Examples of Multiple Alleles:
Blood Types
Types of Corn
Feather Color (in some cases)
Multiple Alleles
A good example is the ABO blood grouping system
There are 4 blood types: A, B, AB, & O
I
A
I
B
I
O
B
AB
IA IA
B
I IB
IA IB
IA IO
B
I IO
A
O
IO IO
Practice
A man with type A blood marries a woman with type B blood. If they have a type O child, what must their genotypes be?
Could they also have a type A child?
Answer these questions using a Punnett Square.