Response to Selection in Finite Locus Models with Nonadditive Effects.

Area of Science:

• Quantitative genetics
• Population genetics
• Animal breeding

Background:

• Quantitative-genetic theory predicts decreased additive genetic variation under directional selection.
• Nonadditive genetic effects (dominance, epistasis) may sustain or increase additive variance.
• Understanding these dynamics is crucial for optimizing genetic gain in breeding programs.

Purpose of the Study:

• To test if finite-locus models with additive and nonadditive genetic effects maintain more additive genetic variance (VA) than models with only additive effects.
• To evaluate if models including nonadditive effects achieve larger medium- to long-term genetic gains under truncation selection.
• To compare the efficacy of BLUP-EBV versus phenotypic selection in different genetic models.

Main Methods:

• Simulated four genetic models with additive, dominance, and additive-by-additive epistatic effects.
• Used a simulated genome with 25 chromosomes and 100 bi-allelic QTL.
• Conducted 100 generations of directional truncation selection on a trait with heritability (h2) of 0.1, using either phenotypic values or BLUP-EBV.

Main Results:

• Additive genetic variance (VA) decreased with directional truncation selection, irrespective of nonadditive effects.
• Nonadditive effects had minimal impact on changes in VA but influenced long-term selection response.
• Additive gene action resulted in the highest response among the simulated genetic models.
• BLUP-EBV led to greater fixation of alleles and higher response compared to phenotypic selection across all models.

Conclusions:

• The presence of nonadditive genetic effects had little impact on the decrease of additive variance under directional selection in the simulated scenarios.
• Directional selection consistently reduces additive genetic variance.
• BLUP-EBV is a more effective selection strategy than phenotypic selection for maximizing genetic gain and allele fixation.