Links
Objectives
- 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).