Complex Patterns of Inheritance

By: Shelby Graff

Multiple Alleles

  • Definition: Traits are controlled by more than two alleles for that trait.
  • Offspring Phenotype: There are four or more possible phenotypes.
  • Examples: Human blood types: Have 3 alleles... Ia, Ib, and i. Ia codes for A blood type, Ib codes for B blood type and i codes for O. This allows for there to be 5 different genotypes. Ia i and Ia Ia genotypes are A blood type phenotype, Ib i and Ib Ib genotypes are B blood type phenotype, Ia and Ib genotype is AB blood type phenotype, and ii is O blood type.
C series in dogs: C is required for color while cc yields an albino. The genotypes and phenotypes are- C... expresses color; cch... expresses chinchilla patterned dog; cd... expresses white dog with dark eyes; cb... expresses pale grey dog; c... expresses albino dog. The pattern of dominance is C>cch>cd>cb>c.


Incomplete Dominance

  • Definition: Neither gene has one allele dominate the other.
  • Offspring phenotype: Offspring that are heterozygous express both alleles.
  • Examples: Red, pink, and white flowers (RR, Rr, and rr)
Chicken Colors- Black (bl bl), Blue (Bl bl), and Splash (Bl Bl)



  • Definition: Both alleles are fully expressed. Neither one is dominant nor recessive.
  • Offspring phenotype: Offspring that are heterozygous express both alleles.
  • Examples: Red flower crossed with white flower produces a white/red spots. (NOT pink.)

AB blood type. The heterozygous AB genotype produces a new blood type, AB. (Both alleles are expressed.


Polygenic Traits

  • Definition: Trait is controlled by several genes. (The genes may be on the same chromosomes or different ones.)
  • Offspring phenotype: Phenotypes are in a wide range. Many different physical traits are possible.
  • Examples: Height, skin color, and weight.