Non Mendelian Genetics Patterns of inheritance that aren’t simply dominant or recessive EQ: What are the differences between various complex inheritance patterns?

I. Incomplete Dominance The phenotype of a heterozygous individual is “blended” between those of the two alleles. B. Examples 1. Snap Dragons – When red and white flowers are crossed – all the F1 (first generation) offspring will have pink flowers 2. Horses – When a chestnut colored horse is bred with a cremello (white) colored horse; the offspring are palomino color.

P=Parent generation F1= First generation of offspring F2= second generation of offspring

II. Co-dominance The phenotypes of both alleles are expressed completely and separately; both alleles are expressed equally. B. Examples 1. Short-horned cattle – red and white coats are co-dominant 2. Chickens – feather color; black and white are co-dominant 3. Four o’clock plants – red and white petals are co-dominant

Four o’clock plants Short-horned cattle Black and white feathers

III. Multiple Alleles Traits controlled by more than 2 alleles. B. Examples 1. ABO blood type in humans – A and B are codominant, but dominant to O 2. Pigeons – feather color; BA, B and b; BA produces ash red feathers, B produces wild-type (grey) feathers, and b produces chocolate colored feathers

IV. Polygenic Inheritance Many traits are controlled by 2 or more genes. B. Examples: 1. Eye color 2. Hair color 3. Skin color 4. Height 5. Fingerprints

Eye Color

Skin Color

V. Traits Influenced by the Environment An individuals phenotype often depends on conditions in the environment. B. Such factors as temperature, amount of sunlight, soil conditions and nutrition can affect the phenotype of an organism. C. Examples: 1. Arctic fox – brown in summer; white in winter 2. Hydrangea flower color – acidity of the soil determines blue or reddish color 3. Siamese cats – cooler body areas are darker 4. Height in humans - early nutrition (or lack of) affects the height of humans