1. Complex Patterns of Inheritance
Exceptions to Mendel’s rules:
not simple dominant/recessive inheritance

2. The phenotype of the heterozygote is INTERMEDIATE.
Incomplete Dominance
The phenotype of the heterozygote is INTERMEDIATE.
Red + White = Pink

3. Red parent plant R R
RR’ R’
White parent plant R’
All pink offspring!

4. Codominance Both alleles are expressed! Red + White =
Both Red and White (NOT pink!)

5. Pleiotropy
The ability of a gene to affect an organism in many ways, not just in one way.
Example: Human disease PKU (phenylketonuria)
Causes mental retardation and reduced skin & hair pigmentation
Caused by mutation in gene for creating the enzyme that breaks down the amino acid phenylalanine
This mutation makes the person unable to break down phenylalanine, leading to toxic levels that can damage the body in many ways.
PKU is manageable with medications and by following a diet free of phenylalanine.

6. PKU patient

7. Epistasis
A gene at one location affects the expression of a gene at another location.
Coat color in mice:
BB & Bb (black)
bb (brown)
Gene that allows color to be deposited:
CC & Cc (color is present)
cc (albino)

9. This is a gene that is controlled by more than two forms of an allele
Multiple Alleles
This is a gene that is controlled by more than two forms of an allele
Blood Types: A, B, AB, O
A and B are codominant
O is recessive to both

11. Type A: IAIA or IAi Type B: IBIB or IBi
Type AB: IAIB Type O: ii

13. Trait controlled by two or more GENES
Polygenic Traits
Trait controlled by two or more GENES
(not alleles)
AaBbCc x AaBbCc
Skin Pigmentation
Height

14. Sex-Linked Traits Humans have 46 chromosomes
22 pairs autosomes (pairs 1-22)
1 pair sex chromosomes (pair #23)
Males: XY Females: XX
Sex-Linked traits are located on the X chromosome. These traits tend to affect males more than females. WHY??
Baldness

15. Colorblindness is a sex-linked trait.
People with normal vision should see a light image of a red/brown sailboat.