1. Exceptions to Mendel’s Laws
Mendel was confused by some of his crosses but there was not enough information available for him to “get it”

2. Single gene inheritance that does not follow the rules of the Principle of Dominance

3. Incomplete Dominance
Wavy Hair
Cream colored
guinea pigs
Pink Flowers

4. Snapdragons show Incomplete DominanceX
WW = white
RR = red
WR = pink
Blending of Alleles - Both alleles contribute
equally to the phenotype, no dominance

5. Codominance
Sickle Cell
Disease
Roan Coat Color
Speckled Chickens

6. Codominance X BB = black BW = speckled WW = white
Both alleles contribute equally to the phenotype
(no blending), white feathers and black feathers

7. Multiple Alleles Human ABO Blood Types 4 Blood Types: A, B, AB, O
1 Gene with 2 alleles, single gene inheritance BUT in the population there are other alleles possible

8. Beyond Single Gene Inheritance
Polygenic - many genes that may or may not follow the rules of the Principle of Dominance

9. Polygenic Traits
Many genes with many different alleles contribute to the phenotype
Hair color, eye color, height, skin color