1. COMPLEX PATTERNS OF HEREDITY
Polygenic Traits:
traits influenced by several genes
ex: human eye color, height, weight, hair color

2. Incomplete Dominance – a trait that is intermediate between the two parents
ex: snapdragons - red flower is crossed with a white flower and pink flowers are produced
RR – red Rr – pink rr – white
ex: in humans straight hair crossed with curly hair may produce wavy hair
SS – straight Ss – wavy ss – curly

3. Incomplete Dominance:
Suppose a red flower is crossed with a pink flower. What are the chances the offspring will have red flowers? Pink flowers? White flowers?
50%
50% 0% R R R RR RR r Rr Rr

4. Codominance – two dominant traits are expressed at the same time
ex: a horse with a black coat is crossed with a horse that has a white coat producing a horse that has both a black and white coat
BB – black BW – black & white WW - white

5. Codominance: B B W BW BW W BW BW
Suppose a horse with a black coat is crossed with a horse with a white coat. What are the chances the offspring will have a black coat? White coat? Black and white coat? 0% 0% B B
100% W BW BW W BW BW

6. Multiple Alleles – genes with 3 or more alleles
ex: 3 alleles – A, B, O
4 blood types – A, B, AB, O
*Even for traits controlled by genes with multiple alleles, an individual can have only 2 of the possible alleles.

7. Blood type inheritance is somewhat complicated, with three forms of the gene (A,B,O), 6 possible genotypes, and 4 possible phenotypes. (A, B, AB, O) AB
AA - Homozygous A
AO - Heterozygous A
BB - Homozygous B
BO - Heterozygous B OO

8. A B B O AB BB AO BO Blood Types: 25% 50% 25%
Suppose a woman with blood type AB marries a man who is heterozygous B. What are the chances that their children will have blood type A?
blood type B?
blood type AB?
25%
A B
50%
25% B O AB BB AO BO

9. Traits Influenced by the Environment:
hydrangea plants: acidic soil – blue flowers
basic soil – pink flowers
arctic fox: summer – produces enzymes that
make pigments therefore it has a
reddish brown coat
winter – pigment producing genes
do not function therefore the coat
of the fox is white

10. Siamese cats: fur color is influenced by
body temperature
cold – dark coat
warm – light coat
humans: height - influenced by nutrition
skin – exposure to the sun