1. Section 7-2: Write everything that is underlined
“Complex Inheritance”
1) Incomplete Dominance
2) Co-Dominance
3) Multiple Alleles
4) Polygenic Traits
Write everything that is underlined

2. KEY CONCEPT Many phenotypes are not explained by the Mendel’s “simple” dominance.

3. Phenotype can depend on interactions of alleles.
1) In Incomplete Dominance, neither allele is completely dominant nor completely recessive.
The heterozygous phenotype is intermediate between the two homozygous phenotypes
The homozygous parental phenotypes are not seen in F1 offspring. (There are 3 phenotypes.)

4. Example: Incomplete Dominance: 4 O’Clock Flowers
The parents’ genotypes are purebred
(homozygous) and are red & white,
but the offspring’s phenotypes are neither
red nor white.
The F1 generation’s genotypes are
all hybrid (heterozygous), but
their phenotype is pink,
a mix or “intermediate”
phenotype.
Copy Diagram 
On back

5. 2) In Codominance, both alleles will be completely expressed to produce a third genotype showing both phenotypes.
Codominant alleles are neither dominant nor recessive.
Ex: Roan Cattle; and the A-B-O blood types result from codominant alleles.
Roan Cattle
Blood Types A and B are Codominant

6. Example of Codominance: Blood Type
There are 3 alleles: A, B, and O
A and B are codominant
O is recessive to A and B
How many genotypes and phenotypes does this make?
Copy column headings
and columns 1 and 3 

7. Multiple Alleles
Many genes have more than two alleles (“multiple alleles”)
- Blood Type: A, B, & O alleles

8. Many genes may interact to produce one trait.
3) Polygenic traits are produced by two or more genes acting together.
Ex: Eye color (3 genes)
Order of dominance: brown > green > blue.

9. Epistatic Genes: an “epistatic” gene can interfere with other genes.
- One or more genes can affect the expression of other genes

10. 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
- nutrition, diseases