Complex Patterns of Inheritance

Jacob Caldwell Isaac Oesterling


  • Definition: Where there is two alleles one dominant, one recessive. The dominant covers up the recessive.
  • Example Organism and Trait: Human, eye color, brown is dominant to blue

  • Ex. problem: A heterozygous brown eyed parent, mates with a homozygous blue eyed parent. What are the possible genotypes?
  • A. BB, bb
  • B. bb
  • C. Bb, bb
  • D. Bb

Multiple Alleles

  • Definition: Traits controlled by more than one allele
  • Offspring Phenotype: Multiple phenotypes
  • Example Organism and Trait: Human, Blood type: A, B, AB, O.

  • Ex. Problem: Someone with O type blood mates with someone with blood type A.What are the possible phenotypes?
  • A. 25%A 75%B
  • B. 100%A
  • C. 50%B 50%O
  • D. 50%A 50%O

Incomplete Domincance

  • Definition: There is not a specific dominant allele, neither allele is expressed over its pair.
  • Offspring Phenotype: In heterozygous incomplete dominant it produces a mix of the two traits rather than one masking the other.
  • Example Organism and Trait: Cross pollination with snapdragon plants one being red one being white, producing a pink flower. A child's wavy hair comes from one parent having straight hair and one having curly hair.

  • Ex. Problem: If a homozygous white flower mates with a pink flower what will the possible phenotypes?
  • A. WW, RW
  • B. RR, WW
  • C. RW
  • D. RW, RR
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  • Definition: Both alleles are fully expressed
  • Offspring Phenotype: Heterozygous offspring exhibit both alleles
  • Example Organism and Trait: The sickle cell and chickens with black and white feathers.

  • Ex. Problem: If a speckled Guinea pig mated with a homozygous black guinea pig what are the possible phenotypes?
  • A. BB, BW
  • B. BW
  • C. WW
  • D. BW, WW

Polygenic Traits

  • Definition: Traits controlled by two or more genes not just alleles
  • Offspring Phenotype: Phenotype is a range
  • Example Organism and Trait: Human height and skin color

  • Ex. Problem: If two very tall parents have a baby, will it most likely be tall or short?
  • A. Tall
  • B. Short
  • C. Cucumber
  • D. FireTruck

Answer Key

  1. C
  2. D
  3. A
  4. A
  5. A