Selection ratio is a useful measure of the effectiveness of selection programs designed to improve the quality of a population. It is defined as the ratio of the difference between the average performance of the offspring of the selected individuals and the average performance of the population before selection, divided by the standard deviation of the population before selection (Van Vleck, 1980). Selection ratio is a measure of the intensity of selection and is used to estimate the expected response to selection.
Selection ratios are commonly used in animal and plant breeding programs. For example, animal breeders often use selection ratios to evaluate the effectiveness of their selection programs for milk yield or egg production. Plant breeders use selection ratios to evaluate the effectiveness of their selection programs for traits such as yield, disease resistance, and drought tolerance (McDonald & Brink, 1988).
Selection ratio can be calculated using the following formula:
Selection Ratio = (Mean of Selected Group – Mean of Unselected Group) / (Standard Deviation of Unselected Group)
The selection ratio can be used to estimate the expected response to selection. A selection ratio of 0.5 indicates that the expected response to selection is half of the standard deviation of the population before selection. A selection ratio of 1.0 indicates that the expected response to selection is equal to the standard deviation of the population before selection (Van Vleck, 1980).
Selection ratios have several advantages over other measures of selection intensity. First, they provide a measure of the intensity of selection that is independent of the size of the population. Second, they provide a measure of the expected response to selection that is independent of the actual performance of the population. Finally, they can be used to compare the intensity of selection for different populations or for different traits (McDonald & Brink, 1988).
In conclusion, selection ratio is a useful measure of the intensity of selection and can be used to estimate the expected response to selection. It is an important tool for animal and plant breeders to assess the effectiveness of their selection programs.
References
McDonald, P., & Brink, D. W. (1988). Animal Breeding Plans (3rd ed.). Ames, IA: Iowa State University Press.
Van Vleck, L. D. (1980). Selection Ratios. Journal of Animal Science, 51(3), 857-865.