Complex Patterns of Inheritance

Emily Tester

Multiple Alleles

  • Three or more alternative forms of a gene (alleles) that can occupy the same locus.

  • Ex) ABO system of blood groups is controlled by three alleles, only two of which are present in an individual.
  • Ex) A,B, & O are alleles.



  • Offspring Phenotype: If one parent has blood type A and the other parent has blood type B, then the offspring would most likely have AB.

Incomplete Dominance

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


  • Ex) The snapdragon flower color is either homozygous for red or white.
  • Ex) A brown fur coat on a rabbit as a result of one rabbit's red allele and one rabbit's white allele not dominating.

  • Offspring Phenotype: If one flower is red and the other is white, than the offspring would be pink.
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Codominance

  • Relationship between two versions of a gene. Individuals receive one version of a gene, called an allele, from each parent. If the alleles are different, the dominant allele usually will be expressed, while the effect of the other allele, called recessive, is masked.


  • Ex) If a person is type O, it means that neither the type A or type B allele is dominant. However, if a person is type AB, this means that both the A allele and the B allele are equally expressed and are therefore codominant.
  • Ex) Chickens with spots on them is also an example because both of the parents traits show up.



  • Offspring Phenotype: If a parent chicken had spots and the other parent chicken was dark, than the offspring would have dark spots.
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Polygenic Traits

  • Polygenic inheritance occurs when one characteristic is controlled by two or more genes. Often the genes are large in quantity but small in effect.


  • Ex) Height and skin color.
  • Ex) Eye color and weight.



  • Offspring Phenotype: If one parent is really tall and the other is short, than the offspring could be either because there are many factors when it comes to height. So the offspring could be any height.
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