1. NOTES 22 – Complex Inheritance Patterns
Most human traits have more than 2 or 3 forms. Types of inheritance that are more complex than simple dominance, incomplete dominance or codominance control these traits.

2. Multiple Allelic Inheritance (Multiple Alleles)
Traits are controlled by 1 gene with more than 2 alleles
Ex. Blood Type in humans
The gene that controls blood type has 3 alleles
A = Type A blood B = Type B blood o = Type O Blood
Alleles A and B are codominant and allele o is recessive

3. There are 6 possible genotypes and 4 possible phenotypes:
A A or A o = Type A Blood
B B or B o = Type B Blood
AB = Type AB Blood
o o = Type O Blood

4. Blood Cells

5. There are four basic Blood types:
Type A with A antigens on the red cells and anti B antibodies in the plasma.
Type B with B antigens on the red cells and anti A antibodies in the plasma.
Type AB with both A and B antigens on the red cells and no blood type antibodies in the plasma.
Type O with no antigens on the red cells and both anti A and anti B antibodies in the plasma

6. Polygenic Inheritance
Traits are controlled by more than 1 gene
There are many possible phenotypes
Ex. Skin color is controlled by at least 3 genes
A = dark skin a = light skin
B = dark skin b = light skin
C = dark skin c = light skin

7. Differences in skin color are largely due to differences in the amount of melanin, a dark pigment produced by skin cells.
Each “dark skin” allele (A, B, C) codes for high melanin production
Each “light skin” allele (a, b, c) codes for low melanin production
Each dark skin allele (A, B, C) in the genotype adds a small but equal amount of pigment to the skin

8. Some possible genotypes and phenotypes:
aabbcc = very light skin
AABBCC = very dark skin
AaBbCc = medium skin

9. What would a Punnett Square for skin color look like?
Cross two medium skin tone parents
AaBbCc X AaBbCc
Each parent could produce 8 different possible combination to pass on: ABC, ABc, AbC, Abc, aBC, aBc, abC, or abc