Ratio of Selection Differential to Standard Deviation

The ratio of selection differential to the phenotypic standard deviation of a trait is known as-

Correct Answer: Intensity of selection

The Intensity of selection (i) is the standardised selection differential — the selection differential (S) expressed in units of phenotypic standard deviation (σP).

Formula

i = S / σP, therefore S = i × σP

Response to Selection — Breeder's Equation

• R = h² × S = i × h² × σP = i × σA × rAP

Factors Affecting Intensity of Selection (i)

• Proportion of population selected (lower proportion → higher i)
• Phenotypic standard deviation (σP)
• Sex of animal under selection
• Number of traits under selection
• Accuracy of trait measurement

Factors Affecting Response to Selection (R)

• Intensity of selection (i)
• Additive genetic variance (σA)
• Accuracy of selection (rAP)
• Population size
• Generation interval