1. 6C. Patterns of Inheritance (Part 2 – Codominant & Incomplete Traits)
Chapter 7.1 & 7.2

2. Incomplete Dominance
In incomplete dominance, neither allele is completely dominant nor completely recessive.
B = Blue and b = Green
BB = Blue
bb = green
Bb = Teal
When both alleles are present (heterozygous) the traits blend
Sometimes, you may use two different letters
Example: B = Blue G= Green

3. Codominance
In codominance, both alleles are dominant.
B = Yellow and b = Black
BB = Yellow
bb = black
Bb = Yellow & Black
When both alleles are present (heterozygous) then both traits show
Sometimes, you may use two different letters
Example: Y = Yellow B= Black

4. Review & Compare Red Pig Red & Blue Pig Purple Pig In Flying Pigs
A = Red a = Blue
If the trait was normal inheritance, what would the phenotype be for a “Aa”?
Red Pig
If the trait was Codominant, what would the phenotype be for a “Aa”?
Red & Blue Pig
If the trait was Incomplete Dominance, what would the phenotype be for a “Aa”?
Purple Pig

5. Many genes may interact to produce one trait.
Polygenic traits are produced by two or more genes.
Example – AaBbCCDd code for one phenotype
Order of dominance: brown > green > blue.

6. AaBb aaBb Aabb aabb Black Yellow Chocolate Yellow
An epistatic gene can interfere with other genes.
For example – in Labs you can have either a Black, yellow or chocolate lab
B = Black b= Chocolate
BUT a = yellow and it is epistatic, which means if the dog inherits a “a” the dog is yellow, it doesn’t matter what if they are BB, Bb, bb
What color is the dog?
AaBb
Black
aaBb
Yellow
Aabb
Chocolate
aabb
Yellow

7. The environment interacts with genotype.
Phenotype is a combination of genotype and environment.
The sex of sea turtles depends on both genes and the environment
Height is an example of a phenotype strongly affected by the environment.