1. Incomplete Dominance
&
Codominance

2. Codominance red white roan
Defined: when a single gene has more than one dominant allele
Ex: Cattle Coat
Red cow x White cow =
Myth: Colors blend
Reality: Both colors are equally seen
Ex: Human Blood types
Type A x Type B = Type AB
red
white
roan

3. Ways of writing blood types
ii – Type O blood
IAIB – Type AB blood
IAIi or IAIA – Type AO blood or Type A blood
IBIi or IBIB – Type BO blood or Type A blood

4. Blood Types Human blood type has 3 alleles Dominant A allele
Dominant B allele
Recessive O allele
Type A & Type B are dominant to type O (recessive)
Type A and Type B are codominant to each other
Dad will pass 1 of these 3
Mom will pass 1 of these 3
Child genotypes
Type A
Type AB
Type A
Type AB
Type B
Type B
Type A
Type B
Type O

5. 1 minute: Discuss with your neighbor
1 minute: Discuss with your neighbor. Mike is heterozygous for type A blood and Lisa is heterozygous for type B blood.
A) Probability of child having type A blood?
25%
B) Probability of child having codominant blood?
C) Probability of child being Heterozygous?
75%
B o A o A B A o B o o o

6. 1 minute: Discuss with your neighbor
1 minute: Discuss with your neighbor. Jason is homozygous for type A blood and Maria who is heterozygous for type B blood. Their child, Rick, has codominant blood.
Type A
Type B
Draw a pedigree for this family.
Complete a Punnett square for Jason and Maria.
What were the odds of Rick having codominant blood?
50% AA
Jason
Maria BB Ao Bo
Rick
Codominant? AB
B o A A B A o A B A o

7. Notice: only time we use 2 letters!
Incomplete Dominance
Notice: only time we use 2 letters! P P PP P P p p pp p p
Red
(RR)
White
(WW)
Pink
(RW)
Defined: Neither allele is completely dominant
Heterozygous = blended appearance
More than 2 different phenotypes can occur
Ex: Many flower colors

8. B Y B B B Y B blue green B B B Y blue green
In a certain species of fish, blue scales (BB) and yellow (YY) scales are incompletely dominant. Fill in the Punnett square with the genotype of a blue male and a green female.
What is the probability of obtaining heterozygous fish?
Yellow fish?
B Y B B B Y
50% B
blue
green B B B Y 0%
blue
green

9. Carnations show incomplete dominance where a red allele and white allele blend to make pink. A pink colored male pollinated a pink colored female. 7 seeds were created and later grew into plants with 3 having pink flowers, 2 with white flowers, and 2 with red flowers.
Create a pedigree for these 9 flowers (make the offspring any gender you wish).
Create a Punnett square for the parents.
Probability of growing pink? RW RW RW RW RW WW WW RR RR
R W R R R R R R W W R W R R W W W W
50%

10. Incomplete vs. Codominance
Codominance: Both equally expressed
Red flowers + White flowers =
Incomplete Dominance: alleles blend