1. Exceptions to Mendel’s Rules
Mendelian Exceptions
Exceptions to Mendel’s Rules

2. Incomplete Dominance
When the heterozygous genotype of a trait shows neither a dominant or recessive phenotype, but rather a mixture.
Ex. Carnation flowers – dominant red allele and recessive white allele results in pink phenotype

3. Incomplete Dominance
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4. Incomplete Dominance

5. Codominance
When the heterozygous genotype expresses both the dominant and recessive phenotypes at the same time
Ex. Blood types – this is how you can have an AB blood type
Sickle-Cell Anemia

6. Codominance Codominant Blood Type A Blood Type AB (Codominant)
Blood Type O
Blood Type B
Blood
Type A
Type B
O allele
B allele
A allele
U.S. National Library of Medicine

7. Multiple Alleles
More than two different alleles can exist for a particular trait, but only two can be present at any given time.
Ex. Blood Types –
This is how you can have A, B, AB, or O type blood.
Phenotype
Genotypes
O ii
A IAIA, IAi
B IBIB, IBi
AB IAIB

8. A O B AB BO O AO OO Blood Type Cross Parents: AO x BO
Offspring Phenotypes:
¼ Type A
¼ Type B
¼ Type AB
¼ Type O B AB BO O AO OO

9. Blood Type Cross I A I B I B I A B I B i I A i I B i

10. Polygenic Inheritance
When a phenotypic result is controlled by the added results of the effects of many genes
Examples:
Height
Weight
Skin Color
Hair Color
Eye Color

11. Polygenic Inheritance
P generation X
aabbcc
AABBCC
(very light)
(very dark) X
F1 generation
AaBbCc AaBbCc