Complex Patterns of Inheritance

Simple Inheritance Mendel studied simple patterns of inheritance. Found that inheritance was controlled by a dominant allele (B) or recessive allele (b). However, there are many inheritance patterns that are more complex. Most traits aren’t simply dominant or recessive.

Incomplete Dominance Heterozygous & Homozygous dominant individuals both have the same phenotype. Example --- Brown eyes= Dominant (B); Blue eyes = Recessive (b) Individual with BB or Bb have what color eyes? Brown

Incomplete Dominance Cont. When traits are inherited in an incomplete dominance pattern, the phenotype of the heterozygous is between the pure dominant (BB) and the pure recessive (bb).

Codominance Codominant alleles --- Both alleles are expressed equally. Example --- when a certain variety of black chicken is crossed with a white chicken, all offspring are checkered (black & white). Both feather colors are produced by codominant alleles.

Multiple Alleles Multiple alleles --- traits controlled by more than 2 alleles. Example of a trait controlled by multiple alleles is blood type.