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

2. 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

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:
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

4. 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

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

6. 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

7. 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

8. 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

9. Blood Type (phenotype)
Example 2:
Blood type in humans is an example of both codominance and multiple alleles. 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
IAIA or IAi B
IBIB or IBi AB
IAIB O ii

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

11. Determine the possible blood types of the offspring when:
2. Mother is type AB, Father is Type A (heterozygous)
Genotypic Ratio:
25 % IAIA % IAi
25% IAIB % IBi
Phenotypic Ratio:
50% Type A Blood
25% Type AB Blood
25% Type B Blood
IA IB
IAIA
IAIB
IAi
IBi IA i

12. Determine the possible blood types of the offspring when:
3. Mother is type A (heterozygous), Father is type B (heterozygous)
Genotypic Ratio:
25 % ii % IAi 25% IAIB % IBi
Phenotypic Ratio:
25% Type O Blood 25% Type A Blood % Type AB Blood 25% Type B Blood
IA i
IAIB
IBi
IAi ii IB i

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

14. Multiple Alleles Multiple alleles mean multiple phenotypes.
Ex: Rabbits have four alleles for coat color. C is dominant to cch which is dominant to ch which is dominant to c.
Two alleles means three genotypes and only two phenotypes, but four alleles mean ten genotypes and five or more possible phenotypes.

15. Epistasis
Epistasis occurs when a gene at one location affects a gene at another location.
Ex: Coat color in adorable ponies
B codes for coat color. B= brown, b=tan.
C codes for presence of pigment. C=pigment present, c=pigment absent.

16. Polygenic Traits Single traits controlled by more than one gene.
Many human traits are polygenic, which explains the variation in human traits.
Ex. Eye color, height, skin color