Analyses of genetic variation now involve nucleotide data, which can be used in a variety of statistical tests to discriminate between patterns of variation due to neutral processes (drift, population expansion, bottlenecks) and various types of selection (positive, purifying, balancing).
Tajima's D test compares two estimators of the mutation parameter θ, Watterson's estimator θs and Tajima's estimator θπ, and significant D values can be due to factors such as population expansion, bottlenecks and selection [ 39].
The prediction of this null hypothesis of no gene flow holds regardless of population expansions, bottlenecks, or substructure that might have occurred in modern human history (SOM Text 15).
Both statistics maintained high power across all of our demographic models, though iHS was more sensitive to expansions, bottlenecks, and migration.
Tajima's D [ 43] und Fu's Fs [ 44] are known to be sensitive to departures from mutation-drift equilibrium due to population size changes (expansions, bottlenecks) and selection.
Tajima's D is significantly positive in both cultivated and wild carrots, although it is higher in cultivated carrot (Table 2), which could be due to genetic bottlenecks, population expansion after bottlenecks, balancing selection, and/or introgression.
In what follows, we will refer to this model as to the "RAOEB" model (i.e. Recent African Origin with Expansion and Bottleneck").
In contrast, the global population exhibits signs of recent expansion and/or bottleneck, such as (i) low genetic diversity and high clonality, (ii) association with the non-native, ubiquitous avian ecological niche, and (iii) lack of geographic structure.
Under the assumption of neutrality, deviations in Tajima's D [ 113] and Fu's Fs [ 114] were used to test for a recent population expansion or bottleneck [ 115].
While the tendering process cannot be shortened to accommodate the training institution expansion, this bottleneck could be addressed by hiring additional staff at the Ministry of Works and Supply.
