When Genetics is Not Simple Other patterns of inheritance

It’s not so Simple Not all traits are controlled by single genes with simple dominant - recessive alleles: Multiple alleles Polygenic traits Incomplete dominance Codominance

Multiple Alleles More than two alleles exist for a particular trait (multiple flavors) Labeled using a single letter and superscripts Results in many possible phenotypes Ex: Human blood types IA, IB, or i

Polygenic Traits More than one gene controls a particular trait Very complicated hereditary patterns Results in an vast array of possible phenotypes Ex: human skin, eye, and hair color

Incomplete dominance One allele is not completely dominant over the other Heterozygous individuals show a trait that is an intermediate or blend of the two homozygous trait Neither homozygous trait shows

Incomplete dominance Example: Four o’clock flowers RR = red flowers WW = white flowers RW = Pink is a blend of red and white

Codominance Both alleles are dominant Both homozygous traits show in heterozygous individuals There is no blending of traits Results in blotches of colors

Codominance Example: Feather color in chickens BB = black feathers WW = white feathers BW = No gray! Both colors “Checkered Chicken”

Codominance Example: Feather color in chickens BB = black feathers WW = white feathers BW = No gray! Both colors “Checkered Chicken”