[1] Its name reflects that QST was intended to be analogous to the fixation index for a single genetic locus (FST).
[2][3] QST is often compared with FST of neutral loci to test if variation in a quantitative trait is a result of divergent selection or genetic drift, an analysis known as QST–FST comparisons.
QST represents the proportion of variance among subpopulations, and is it’s calculation is synonymous to FST developed by Sewall Wright.
[4] However, instead of using genetic differentiation, QST is calculated by finding the variance of a quantitative trait within and among subpopulations, and for the total population.
Calculation of QST is subject to several assumptions: populations must be in Hardy-Weinberg Equilibrium, observed variation is assumed to be due to additive genetic effects only, selection and linkage disequilibrium are not present,[5] and the subpopulations exist within an island model.
If QST is found to exceed FST, this is interpreted as evidence of divergent selection, because it indicates more differentiation in the trait than could be produced solely by genetic drift.
If the values of QST and FSTare equivalent, the observed trait differentiation could be due to genetic drift.
[13] In an ecological restoration study, Bower and Aitken used QST to evaluate suitable populations for seed transfer of whitebark pine.
[11] In an examination of the common snapdragon (Antirrhinum majus) along an elevation gradient, QST-FST analyses revealed different adaptation trends between two subspecies (A. m. pseudomajus and A. m. striatum).
While both subspecies occur at all elevations, A. m. striatum had high QST values for traits associated with altitude adaptation: plant height, number of branches, and internode length.