1. Incomplete Dominance Codominance Multiple Alleles
(A.K.A. – Non-Mendelian Inheritance)

2. Review: Dominant/Recessive
One allele is dominant over the other (capable of “hiding” the recessive allele)

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. What does Non-Mendelian mean?
Not all traits are as simple as dominant and recessive
Some traits…
Have 2 dominant alleles
Have more than 2 alleles or variations.
Are only passed on by the sex chromosomes.
Are the result of 100’s of genes being expressed

5. Incomplete Dominance
A third (new) phenotype appears in the heterozygous condition.
Flower Color in snapdragons, four o’clocks, carnations

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

7. Codominance
The heterozygous condition, both alleles are expressed equally
Ex) Sickle cell anemia, Roan colouration

9. Problem: Codominance
Show the cross between an individual with fatal sickle-cell anemia and another who is a carrier but not sick.
N S
GENOTYPES:
- NS (2) SS (2)
- ratio 1:1 S NS SS
PHENOTYPES:
- carrier (2); sick (2)
- ratio 1:1

10. Multiple Alleles There are more than two alleles for a trait.
Ex.) The ABO blood types result from
multiple alleles that are codominant

11. Human blood type has 3 alleles:
Dominant A (IA)
Dominant B (IB)
Recessive O (i)
A and B alleles are codominant

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

15. Problem: Multiple Alleles
Show the cross between a mother who has type O blood and a father who has type AB blood.
A B
GENOTYPES:
- AO (2) BO (2)
- ratio 1:1 O AO BO
PHENOTYPES:
- type A (2); type B (2)
- ratio 1:1

16. Problem: 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
AB (1); BO (1);
AO (1); OO (1)
- ratio 1:1:1:1 B O AB OO BO AO
PHENOTYPES:
type AB (1); type B (1)
type A (1); type O (1)
- ratio 1:1:1:1

17. Polygenic Traits A trait controlled by more than 2 genes
Ex.) Human skin, eye, & hair colour

19. Ex.) Labrador retriever coat colour
An epistatic gene can interfere with other genes by overshadowing them for a particular trait.
Ex.) Labrador retriever coat colour
Black (B) is dominant over chocolate (b)
Yellow (E or e) is recessive epistatic (meaning when “ee” is present, it blocks the expression of black and chocolate alleles)

21. Last thing…the environment!
The environment can affect phenotype
Ex.) Sex of sea turtles depends on both genes and temperature

22. versus