In biological classification systems, many species can be divided into subspecies (or biological races, a less common term for subspecies). At what point are two populations in a species different enough to be divided into subspecies? Scientists analyze the distribution of genetic variants (polymorphisms) between populations to determine how different they are from each other. The fixation index (denoted as FST) is a statistical measure that quantifies these differences. FST measures a ratio of genetic variation in a species’ subpopulations in relation to total species genetic variation. If populations within a species exhibit the same polymorphisms at all of its gene locations, the FST will be 0.000. If populations are completely different in their polymorphisms, the FST value will be 1.000. Interact with this slider widget to see what an increase in the average FST between populations means for different species.
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