Complex Patterns of Inheritance

Emma Cordes & Daniel Kahil

Multiple Alleles

Definition: traits that are controlled by more than two alleles

Phenotype of Offspring: multiple offspring phenotypes

Examples: 1) human ABO blood type; humans can have red blood cells that are of type A, type B, or type O. 2) C series in dogs; dogs can have multiple alleles revealing hundreds of different traits.

Incomplete Dominance

Definition: a genetic situation in which one allele does not completely dominate another allele, and therefore results in a new phenotype.

Phenotype of Offspring: intermediate between both parents.

Examples: 1) Snapdragon Flower that is pink as a result of cross-pollination between a red flower and a white flower when neither the red or white alleles are dominant. 2) A blue bird and a red bird mate producing multiple colored offspring.


Definition: when both alleles in a genotype are expressed equally

Phenotype of Offspring: offspring that are heterozygous express the phenotypes of both homozygous genotypes.

Examples: 1) certain cattle or horses coats; when a white homozygous horse mates with a red homozygous horse, the heterozygous offspring ends up with a "roan coat". 2) human blood type (similar to multiple alleles); a human's blood type may be A, B, AB, or O.

Polygenic Traits

Definition: trait is controlled by at least three genes with six alleles.

Phenotype of Offspring: offspring may have a wide range of phenotypes (traits).

Examples: 1) human skin color; in many cases this phenotype is controlled by several different genes. 2) disease resistance; due to the genes certain offspring inherit, it could do well or poorly in resisting illnesses.