1. When Genetics is Not Simple
Other patterns of inheritance

2. It’s not so Simple
Not all traits are controlled by single genes with simple dominant - recessive alleles:
Multiple alleles
Polygenic traits
Incomplete dominance
Codominance

3. Multiple Alleles
More than two alleles exist for a particular trait (multiple flavors)
Labeled using a single letter and superscripts
Results in many possible phenotypes
Ex: Human blood types IA, IB, or i

4. Polygenic Traits More than one gene controls a particular trait
Very complicated hereditary patterns
Results in an vast array of possible phenotypes
Ex: human skin, eye, and hair color

5. Incomplete dominance
One allele is not completely dominant over the other
Heterozygous individuals show a trait that is an intermediate or blend of the two homozygous trait
Neither homozygous trait shows

6. Incomplete dominance Example: Four o’clock flowers RR = red flowers
WW = white flowers
RW =
Pink is a blend of red and white

7. Codominance Both alleles are dominant
Both homozygous traits show in heterozygous individuals
There is no blending of traits
Results in blotches of colors

8. Codominance Example: Feather color in chickens BB = black feathers
WW = white feathers
BW =
No gray! Both colors “Checkered Chicken”

9. Codominance Example: Feather color in chickens BB = black feathers
WW = white feathers
BW =
No gray! Both colors “Checkered Chicken”