Complex Patterns of Complex Patterns of InheritanceInheritance

Simple InheritanceSimple Inheritance

Mendel studied simple patterns of Mendel studied simple patterns of inheritance.inheritance.

Found that inheritance was controlled Found that inheritance was controlled by a dominant allele (B) or recessive by a dominant allele (B) or recessive allele (b).allele (b).

However, there are many inheritance However, there are many inheritance patterns that are more complex.patterns that are more complex.

Most traits aren’t simply dominant or Most traits aren’t simply dominant or recessive.recessive.

Incomplete DominanceIncomplete Dominance

Heterozygous & Homozygous Heterozygous & Homozygous dominant individuals both have the dominant individuals both have the same phenotype.same phenotype.

Example --- Brown eyes= Dominant Example --- Brown eyes= Dominant (B); Blue eyes = Recessive (b)(B); Blue eyes = Recessive (b)

Individual with BB or Bb have what Individual with BB or Bb have what color eyes? Browncolor eyes? Brown

Incomplete Dominance Incomplete Dominance Cont.Cont.

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

CodominanceCodominance

Codominant alleles --- Both alleles Codominant alleles --- Both alleles are expressed equally.are expressed equally.

Example --- when a certain variety of Example --- when a certain variety of black chicken is crossed with a white black chicken is crossed with a white chicken, all offspring are checkered chicken, all offspring are checkered (black & white).(black & white).

Both feather colors are produced by Both feather colors are produced by codominant alleles.codominant alleles.

Multiple AllelesMultiple Alleles

Multiple alleles --- traits controlled by Multiple alleles --- traits controlled by more than 2 alleles.more than 2 alleles.

Example of a trait controlled by Example of a trait controlled by multiple alleles is blood type.multiple alleles is blood type.