The Fixation Index (FST) is the measurement of gene flow, or variance, from genetic markers between fixated groups of animals, most commonly used to measure the relation of genes between animals due to inbreeding. The range of FST is between 0 and 1, with 0 representing no gene differentiation between a single species of animal and 1 representing complete gene differentiation between a single species of animal. An extensive amount of scientific research in the field of genetic biology in animals is helpful in understanding the detailed intricacies of the Fixation Index, but to calculate the Fixation Index of an animal population, only the FST formula and basic mathematical skills are necessary.

Subtract the mean expected heterozygosity within random mating subpopulations (HS) from the expected heterozygosity in random mating total population (HT). This portion of the formula is (HT-HS).

Divide (HT-HS) by HT. This portion of the formula is (HT-HS) / HT.

Round this number to the nearest thousandth (leave only 3 places after the decimal point) to determine FST.

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For more information on how the geneology numbers needed for the FST formula are determined, visit the University of Auckland's Simple Guide to F-Statistics website.