1. Incomplete Dominance Codominance Multiple Alleles
In a nutshell!

2. Review: Dominant/Recessive
One allele is dominant over the other (capable of masking the recessive allele)
PP = purple
Pp = purple
pp = white

3. Review Problem: Dominant/Recessive
In pea plants, purple flowers (P) are dominant over white flowers (p) show the cross between two heterozygous plants.
P p
GENOTYPES:
- PP (1); Pp (2); pp (1)
- ratio 1:2:1 P p PP Pp
PHENOTYPES: Pp pp
- purple (3); white (1)
- ratio 3:1

4. Incomplete Dominance
A third (new) phenotype appears in the heterozygous condition.
This new phenotype is a combination of the dominant and recessive trait.
Example: Flower Color
RR = red
rr = white
Rr = pink

5. Problem: Incomplete Dominance
Show the cross between a pink and a pink flower.
GENOTYPES:
R r
- RR (1); Rr (2); rr (1)
- ratio 1:2:1 R r Rr RR rr
PHENOTYPES:
- red (1); pink (2); white (1)
- ratio 1:2:1

6. Incomplete Dominance Ratios
Incomplete Dominance Genotypic ratio is written as:
Homozygous dominant: Heterozygous: Homozygous recessive
Incomplete Dominance Phenotypic ratio is written as:
Dominant trait: Incomplete trait (mix): recessive trait

7. Codominance NS = some of each NN = normal cells SS = sickle cells
There are more than 1 Dominant allele
The heterozygous condition, both alleles are expressed equally
Example: Sickle Cell Anemia in Humans
NS = some of each
NN = normal cells
SS = sickle cells

8. Codominance There are more than 1 Dominant allele
The heterozygous condition, both alleles are expressed equally
Example: Camilla flowers
RR= Red flowers
WW= White flowers
RW= Red and White flowers

9. Problem: Codominance
Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick.
N S
GENOTYPES:
N/A S NS SS
PHENOTYPES:
N/A

10. Multiple Alleles There are more than two alleles for a trait
Example: Blood type in humans
Blood Types?
Type A, Type B, Type AB, Type O
Blood Alleles?
A, B, O (in book – IA, IB, Io)

11. Rules for Blood Type A and B are codominant O is recessive
AA = Type A
BB = Type B
AB = Type AB
O is recessive
A and B are dominant over O
AO = type A
BO = type B
OO = type O

12. Problem 1: Multiple Alleles
Show the cross between a mother who has type O blood and a father who has type AB blood.
O O
GENOTYPES:
N/A A B AO BO
PHENOTYPES:
N/A

13. Problem 2: Multiple Alleles
Show the cross between a mother who is heterozygous for type B blood and a father who is heterozygous for type A blood.
GENOTYPES:
A O
N/A B O AB OO BO AO
PHENOTYPES:
N/A

14. Review Complete Dominance: Only either Dominant or Recessive in trait
Incomplete Dominance: Dominant, Mixed or Recessive trait
Co-dominance: More than one dominant allele (gene)- each expressed equally
Multiple Alleles: More than two dominant and or recessive alleles- many trait combinations