Other Patterns of Inheritance (11.3)

Exception: Some alleles are neither dominant nor recessive Figure 11-12 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

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

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

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

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