Lesson Plan: Lack of Dominance Biology

This lesson plan includes the objectives and prerequisites of the lesson teaching students how to explain what occurs when alleles do not have complete dominance and interpret Punnett squares that show this.


Students will be able to

  • define lack of dominance as an allele not having complete dominance over another,
  • recall that incomplete dominance and codominance are examples of alleles showing a lack of dominance,
  • describe incomplete dominance as the merging of phenotypes to give a new, distinct phenotype and use the production of pink snapdragon flowers as an example,
  • describe codominance as the simultaneous expression of alleles where both are dominant and use the AB blood group in humans as an example,
  • define multiple alleles as a trait that is determined by three or more alleles where only two are present in a single organism (e.g., alleles for blood types in humans),
  • interpret Punnett squares of incomplete dominance, codominance, and multiple allele crosses.


Students should already be familiar with

  • simple Punnett squares,
  • the fact that alleles can be dominant or recessive.

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