QST (genetics)

In quantitative genetics, QST is a statistic intended to measure the degree of genetic differentiation among populations with regard to a quantitative trait. It was developed by Ken Spitze in 1993. Its name reflects the fact that it was intended to be analogous to the fixation index for a single genetic locus, which is denoted FST. QST is often compared with FST to test the hypothesis that a given quantitative trait has been the subject of divergent selection between the populations being studied. Generally, if QST is found to exceed FST, this is interpreted as evidence of such divergent selection, because it indicates that there is more differentiation in the trait than could be produced solely by genetic drift. By contrast, if the values of QST and FST in the same study are approximately equal, it is considered to reflect that the observed trait differentiation could be entirely due to genetic drift. However, the assumptions on which studies using this methodology (known as QST–FST comparisons) are based have been questioned.