Forward and reverse response to artificial selection.

Area of Science:

• Population Genetics
• Quantitative Genetics
• Animal Breeding

Background:

• Artificial selection is widely used to improve traits in livestock and crops.
• Understanding the long-term effects of selection, including potential reversals, is crucial for sustainable breeding programs.

Purpose of the Study:

• To mathematically describe the impact of reverse selection on genetic gains achieved through prior forward selection.
• To provide a framework for predicting the extent of genetic reversal under different selection scenarios.

Main Methods:

• An additive genetic model was employed for a finite population of effective size N.
• No natural selection was assumed.
• Mathematical expressions were derived to quantify the change in metric mean due to reverse selection relative to forward selection.

Main Results:

• The ratio of response to reverse selection (R) to the response to forward selection (Δx) was expressed in terms of the inbreeding coefficient (F).
• When reverse selection duration equals forward selection duration (t'=t), R/Δx = 1 - F, where F = 1 - (1 - 1/2N)^t.
• For a single generation of reverse selection (t'=1), NR1/Δx is approximately (1-F)/2F, and R/Δx never exceeds t'/t.

Conclusions:

• Reverse selection can significantly reduce or eliminate genetic gains from previous forward selection.
• The effectiveness of reverse selection is influenced by the inbreeding level and the duration of both forward and reverse selection phases.
• These findings have implications for managing genetic resources and designing long-term breeding strategies to avoid unintended genetic erosion.