1. Multiple Alleles & Polygenic Traits

2. The gene for blood type has 3 possible alleles.
Multiple Alleles
In traits with multiple alleles, each individual can carry any two of the several possible alleles.
Ex. BLOOD TYPE
The gene for blood type has 3 possible alleles.
IA, IB, and i

3. Blood Type In this case both IA and IB are dominant to i (recessive).
IA and IB are codominant (both expressed)
So... there are four human blood types
Genotype
Phenotype
IAIA, IAi
Blood type A
IBIB, IBi
Blood type B
IAIB
Blood type AB ii
Blood Type O

4. Multiple Alleles Alleles for blood type are: -IA (dominant)
-IB (dominant)
-i (recessive)

5. Blood Type Practice Problems:
1. A mother is AB and a father is O. Draw the punnett square.
IA IB i
What is the probability their offspring will have A type blood? ____
Can they have an offspring with O blood? ____

6. Blood Type
2. A mother is IAi and a father is IB IB. Draw the punnett square.
What is the probability their offspring will have B type blood?
Can they have an offspring with O blood?

7. Blood Type
3. If a child has AB blood which of the following could NOT be the parents?
a) ii, IAIB
b) IAi, IBIB
c) IBIB, IAIA
d) IAi, IBi

8. Polygenic Traits
Trait is controlled by interaction between 2 or more genes
Examples: skin color, eye color, height, hair color
Results in a continuum of expressed phenotypes

9. Incomplete Dominance
Neither allele is dominant; heterozygote is a blend of phenotypes of the two homozygotes.
Red + White = Pink

10. Codominance Both alleles are dominant; expressed separately
Red + White =
Both Red and White (NOT pink!)