1. Incomplete Dominance
Incomplete Dominance: The heterozygous genotype produces a phenoytype that falls in between the dominant trait and the recessive trait.

2. Codominant vs Incomplete Dominant- What’s the difference?

3. Example:
In flowers, petal color demonstrates incomplete dominance. Red results when a flower has homozygous dominant alleles for the trait. White results when a flower has homozygous recessive alleles for the trait. A flower that is heterozygous for this trait will be pink. Predict the genotypic and phenotypic ratios of the offspring for the following:
1. Red and white RR x rr
Genotypic Ratio:
100% Rr
Phenotypic Ratio:
100% pink flowers
R R Rr r

5. Red= RR
White= WW
RW= pink- each allele is equally expressed to result in a blended product

8. Example:
In flowers, petal color demonstrates incomplete dominance. Red results when a flower has homozygous dominant alleles for the trait. White results when a flower has homozygous recessive alleles for the trait. A flower that is heterozygous for this trait will be pink. Predict the genotypic and phenotypic ratios of the offspring for the following:
2. Red and pink RR x Rr
Genotypic Ratio:
50% RR % Rr
Phenotypic Ratio:
50% Red flowers, 50% Pink flowers
R R RR Rr R r

9. Rr rr RR Rr rr White and Pink rr x Rr r r R r Pink and Pink Rr x Rr
Genotypic Ratio:
50% Rr % rr
Phenotypic Ratio:
50% Pink flowers % White flowers
r r Rr rr R r
Pink and Pink Rr x Rr
Genotypic Ratio:
25% RR % Rr % rr
Phenotypic Ratio:
25% Red flowers % Pink flowers % White flowers
R r RR Rr rr R r

10. Codominance
Codominance: condition in which both alleles of a gene are expressed in heterozygous offspring.

13. Example 1:
In cows black coat color and white coat color are codominant. Heterozygous offspring will be spotted.
Black cow and White cow BB x WW
B B
Genotypic Ratio:
100% BW
Phenotypic Ratio:
100% Spotted cow BW W

14. Codominance
Both alleles are expressed in the phenotype
Ex. Cow Hair Color
RR – Red
WW – White
RW – Roan (Red & White)

16. Example 1:
In cows black coat color and white coat color are codominant. Heterozygous offspring will be spotted.
2. Black cow and Spotted cow BB x BW
B B
Genotypic Ratio:
50% BB % BW
Phenotypic Ratio:
50% Black cow % Spotted cow BB BW B W

17. Example 1:
In cows black coat color and white coat color are codominant. Heterozygous offspring will be spotted.
3. Both Spotted cows BW x BW
Genotypic Ratio:
25 % BB % BW % WW
Phenotypic Ratio:
25% Black cow % Spotted cow % White cow
B W BB BW WW B W

18. Blood Type (phenotype)
Example 2:
In blood typing, the gene for type A and the gene for type B are codominant. The gene for type O is recessive.
Blood Type (phenotype)
Genotype A
AA or AO B
BB or BO AB O OO

20. AO Determine the possible blood types of the offspring when:
1. Mother is type O, Father is type A (homozygous)
O O
Genotypic Ratio:
100% AO
Phenotypic Ratio:
100% Type A Blood AO A

21. AA AB AO BO Determine the possible blood types of the offspring when:
2. Mother is type AB, Father is Type A (heterozygous)
Genotypic Ratio:
25 % AA % AO 25% AB % BO
Phenotypic Ratio:
50% Type A Blood % Type AB Blood 25% Type B Blood
A B AA AB AO BO A O

22. AB BO AO OO Determine the possible blood types of the offspring when:
3. Mother is type A (heterozygous), Father is type B (heterozygous)
Genotypic Ratio:
25 % OO % AO 25% AB % BO
Phenotypic Ratio:
25% Type O Blood 25% Type A Blood % Type AB Blood 25% Type B Blood
A O AB BO AO OO B O

23. AB Determine the possible blood types of the offspring when:
4. Mother is type B (homozygous), Father is type A (homozygous)
B B
Genotypic Ratio:
100% AB
Phenotypic Ratio:
100% Type AB Blood AB A

24. More on blood types…..
The blood type determines what antibodies are located within the blood. Type A blood has type B antibodies. If type B blood is put into their bodies, their immune system reacts as if it were a foreign invader, the antibodies clump the blood - can cause death.
Type AB blood has no antibodies, any blood can be donated to them - they are called the "universal acceptors"
Type O blood has no surface markers on it, antibodies in the blood do not react to type O blood, they are called the "universal donors"