Selection index theory for populations under directional and stabilizing selection.

Area of Science:

• Animal breeding and genetics
• Quantitative genetics
• Livestock production

Background:

• Traditional selection index theory is limited to directional selection, failing to optimize traits with intermediate optima.
• Maximizing breed profit requires considering both directional and stabilizing selection for traits like conformation and product quality.

Purpose of the Study:

• To develop an extended selection index theory that accommodates both directional and stabilizing selection.
• To create an optimum selection index that maximizes breed profit across various selection scenarios.

Main Methods:

• The study extends traditional selection index theory to include stabilizing selection.
• The optimum selection index is formulated to account for breeding values, squared breeding values, and genetic markers (QTL).

Main Results:

• The optimum selection index drives trait means toward optima and decreases phenotypic variance under stabilizing selection.
• The index incorporates breeding values, squared breeding values, QTL allele content and heterozygosity, inbreeding coefficient, and kinship.

Conclusions:

• The optimum selection index promotes fixation of major QTL alleles as trait means approach optima, increasing breed profit.
• Kinship weighting balances genetic gain from outcrossing with gains from reduced variance under stabilizing selection.
• Combining ability emerges as a key parameter for mate allocation to optimize offspring phenotypes.