Mendelian Inheritance

Principles Module 40


  • Describe the relationship between meiosis and genetic crosses
  • Analyze the results of a dihybrid cross

Key points

Principle of Independent Assortment

  • when performing a cross and following 2 traits, the same laws govern this process as for a single trait
  • the 2 alleles for a given gene assort independently of the 2 alleles for another gene
  • just because combinations of alleles were together in the parent doesn’t mean they travel together through inheritance

Dihybrid Cross

  • this kind of cross demonstrates the Principle of Independent Assortment
  • Following 2 characters through a single cross
  • the gametes contain one allele for each character
  • for a dihybrid cross, there are 4 possible combinations of alleles
  • cross 2 lines that are true-breeding for 2 characters, results in the dihybrid, or double-heterozygous, state
  • F1 shows only 2 dominant traits
  • F2 shows all 4 traits again, in 9:3:3:1 proportion

In-class activities

  • work through dihybrid examples

Questions for Practice

  • Diagram a cross between the following true-breeding parents: yellow seeds and purple flowers crossed with green seeds and white flowers (assume yellow is dominant to green and purple is dominant to white).