Complementation

Complementation Test Study Guide

Key Terms & Definitions

  • Allelic mutations (Allelic genes) → Mutations in the same gene.

  • Non-allelic mutations (Non-allelic genes) → Mutations in different genes.

  • Wild-type (WT) strain → A normal strain that can grow on minimal media (prototroph).

  • Auxotrophic strain → A mutant strain that cannot grow on minimal media and requires additional nutrients.

  • Complementation test → A genetic test to determine whether two mutations affect the same gene or different genes.

  • Complementation group → A group of mutants that fail to complement each other, indicating they belong to the same gene.

Steps of a Complementation Test

  1. Cross two haploid mutant strains with identical phenotypes (both auxotrophic).

  2. Grow the resulting diploid strain on minimal media.

  3. Interpret the results:

    • ✅ Growth (Complementation Occurs) → Mutations are non-allelic (in different genes). The diploid is a prototroph.

    • ❌ No Growth (No Complementation) → Mutations are allelic (in the same gene). The diploid remains an auxotroph.

How to Analyze Results

Result

Interpretation

Gene Relationship

✅ Growth on minimal media

Complementation occurs

Mutations are in different genes (non-allelic)

❌ No growth on minimal media

No complementation

Mutations are in the same gene (allelic)

Important Notes

  • The complementation test only works with recessive mutants and haploid mutants.

  • If mutations fail to complement, they belong to the same complementation group and represent the same gene.