1. Other Patterns of Inheritance (11.3)

2. Exception: Some alleles are neither dominant nor recessive
Figure page 319
Parents: RR  red / WW white
F1 generation: RW  pink (When did we use pink flowers?)
Incomplete dominance: one alleles is not completely dominant over another allele
The heterozygous phenotype is somewhere between the two homozygous phenotypes
Incomplete Dominance

3. Codominance: the phenotypes produced by both alleles are clearly expressed
Example: Certain chickens have express codominance in their feather color. Instead of producing a completely black or completely white chicken, both phenotypes show through creating an “erminette” speckled with both black and white feathers.
Example: Many human genes, such as a protein for cholesterol level, show codominance. People with the heterozygous protein produce two different forms of the protein: each affecting cholesterol a different way.
Codominance

4. Exception: Many genes exist in several different forms that have multiple alleles.
Not just A / a
An individual still only has two alleles for every gene inherited, but the variety in the population is greater
Example: Rabbit Fur (4 alleles)
Example: Blood type (3 alleles)
Multiple Alleles

5. Polygenic traits: traits that are controlled by two or more genes
Example: Fruit Fly eyes  at least three different genes control the trait
Example: Skin color in humans  many different genes control the trait
Example: Eye color  may genes control the trait
Wide range of phenotypes
Polygenic Traits

6. Genes and the environment
Genes provide a plan, but the environment controls how it unfolds.
Phenotype is only party determined by its genotype
Environmental conditions can affect gene expression and influence genetically determined traits
Genes + Environment = Phenotype
Example: Buckeye Butterfly
Scientists noticed the butterflies that hatched in the fall had a different wing color compared to those hatching in the summer. Why?
Genes and the environment