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

2. The phenotype of the heterozygote is INTERMEDIATE (a blend!)
Incomplete Dominance
The phenotype of the heterozygote is INTERMEDIATE (a blend!)
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. 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

6. Type A: IAIA or IAi Type B: IBIB or Ibi
Type AB: IAIB Type O: ii

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

9. 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

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