1. Complex Heredity
What Mendel thought was “normal” inheritance is not always the norm
The phenotype can be controlled by many factors
INCOMPLETE DOMINANCE
The dominant allele isn’t “dominant” enough to hide the recessive allele
Produces a blend of 2 phenotypes
Ex: Carnation flowers
Dominant ‘R’ is red
Recessive ‘r’ is white

2. Complex Heredity CODOMINANCE
Both alleles are equally dominant in the Heterozygous state
Ex: Roan Horse
‘R’ is red
‘W’ is white

3. Complex Heredity MULTIPLE ALLELES POLYGENIC TRAITS
Genes have more than just 2 alleles
Ex: Blood Type : A, B, & O blood alleles
POLYGENIC TRAITS
Different genes can control one trait
Human skin color (12 genes); eye color
PLEIOTROPY One gene controls many traits
Ex: Gene for white fur color in cats also controls eyes and ears: most white cats are usually deaf and blue eyed

4. Complex Heredity EPISTASIS LINKAGE CROSSING OVER ENVIRONMENTAL
One gene interferes with another gene
Ex: A gene for albinism will hide a gene controlling hair color
LINKAGE
Many genes located on the same chromosome and won’t separate
CROSSING OVER
Homologues “swap” portions of chromosomes; exchange genes
ENVIRONMENTAL
Radiation: skin color can ‘tan’ during the summer from sun Temperature: arctic fox is brown in the summer; white in the winter