In population genetics, the four-gamete test (FGT) is a method for detecting historical recombination events.
[1] The four gamete-test detects pairs of segregating sites that have arisen either by recombination or by a repeat mutation.
The test is based on an infinite-sites assumption (i.e. repeat mutations have zero probability).
Under this hypothesis, the probability of a repeat mutation is zero, and hence a recombination event is inferred.
The FGT detects recombination events by identifying the type of configuration presented above in the data.