The effect of deviations from steady-state selection responses when generations overlap

ABSTRACTIn populations where generations overlap and initial genetic differences between age groups differ from steady-state values, genetic responses fluctuate in the early years of a selection programme. The degree of deviation of these selection responses from steady-state responses indicates the usefulness of estimates of economic returns calculated more simply using the steady-state value. Here these deviations and their effect on sums of discounted returns are first defined and the models derived then used in numerical analysis. Some problems of definition of these deviations are discussed.The results showed that deviations from sums of discounted returns calculated using steady-state responses varied from about −1% when starting conditions were similar to steady-state conditions to more than 20% when initial genetic differences between age groups were taken as zero. Increases in discount rate increased the effect of the deviations from uniform response while the effect of changing age structure was unpredictable. As initial genetic differences between age groups increased, deviations were increasingly positive among selection methods which made better use of those differences.