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In population genetics, F-statistics (also known as fixation indices) describe the statistically expected level of heterozygosity in a population; more specifically the expected degree of (usually) a reduction in heterozygosity when compared to Hardy–Weinberg expectation.
Fst values between European populations. The fixation index (F ST) is a measure of population differentiation due to genetic structure.It is frequently estimated from genetic polymorphism data, such as single-nucleotide polymorphisms (SNP) or microsatellites.
It is usually associated with other statistical measures of population diversity, and is similar to expected heterozygosity. This statistic may be used to monitor diversity within or between ecological populations, to examine the genetic variation in crops and related species, [3] or to determine evolutionary relationships. [4]
When calculating an allele frequency for a diploid species, remember that homozygous individuals have two copies of an allele, whereas heterozygotes have only one. In our example, each of the 42 pink-flowered heterozygotes has one copy of the a allele, and each of the 9 white-flowered homozygotes has two copies.
Tajima's D is a population genetic test statistic created by and named after the Japanese researcher Fumio Tajima. [1] Tajima's D is computed as the difference between two measures of genetic diversity: the mean number of pairwise differences and the number of segregating sites, each scaled so that they are expected to be the same in a neutrally evolving population of constant size.
One of the most important measures of genomic health is the ratio of expected heterozygosity to measured heterozygosity. Generally, an individual or species with more heterozygous alleles have a higher chance of survival. This is known as heterosis. [4] Low levels of heterozygosity is a sign of possible concern for a species or organism.
In the equation, heterozygosity values expected from the total population are compared to observed heterozygosity values of the sub-populations within this total population. Larger F ST values imply that the level of genetic differentiation between sub-populations within a total population is more significant. [ 26 ]
The value of ′ will be within the range ′. When ′ =, the loci are independent. When ′ <, the alleles are found less often than expected. When < ′, the alleles are found more often than expected.