Index versus tandem selection after repeated generations of selection

Area of Science:

• Quantitative Genetics
• Animal Breeding
• Statistical Genetics

Background:

• Multiple-trait selection is crucial for improving complex traits in breeding programs.
• Index selection and tandem selection are two common methods with differing theoretical efficiencies.
• Understanding long-term selection effects on genetic parameters is vital for sustained genetic gain.

Purpose of the Study:

• To theoretically compare index and tandem selection methods over multiple generations.
• To analyze the impact of changing genetic parameters on selection response.
• To evaluate the efficiency of index selection with constant versus updated weights.

Main Methods:

• Theoretical comparison assuming infinite loci, directional/truncation selection, discrete generations, and infinite population size.
• Derivation of algebraic expressions for asymptotic responses and genetic parameters.
• Recurrence formulae developed to predict genetic parameters and responses per generation.

Main Results:

• Selection-induced linkage disequilibrium alters genetic parameters over generations until equilibrium.
• Constant index weights result in minimal response loss (0-1.5%) compared to updated weights.
• Index selection's relative efficiency over tandem selection decreases with repeated cycles, particularly with high heritability and negative trait correlations.

Conclusions:

• While index selection is initially more efficient, its advantage wanes over extended selection periods.
• The study highlights the dynamic nature of genetic parameters under selection.
• Further considerations like gene frequency changes and finite population size could further reduce index selection's advantage.