Female meiotic drive shapes the distribution of rare inversion polymorphisms in Drosophila melanogaster.

In all species, new chromosomal inversions are constantly being formed by spontaneous rearrangement and then stochastically eliminated from natural populations. In Drosophila, when new chromosomal inversions overlap with a pre-existing inversion in the population, their rate of elimination becomes a function of the relative size, position, and linkage phase of the gene rearrangements. These altered dynamics result from complex meiotic behavior wherein overlapping inversions generate asymmetric dyads that cause both meiotic drive/drag and segmental aneuploidy. In this context, patterns in rare inversion polymorphisms of a natural population can be modeled from the fundamental genetic processes of forming asymmetric dyads via crossing-over in meiosis I and preferential segregation from asymmetric dyads in meiosis II. Here, a mathematical model of crossover-dependent female meiotic drive is developed and parameterized with published experimental data from Drosophila melanogaster laboratory constructs. This mechanism is demonstrated to favor smaller, distal inversions and accelerate the elimination of larger, proximal inversions. Simulated sampling experiments indicate that the paracentric inversions directly observed in natural population surveys of Drosophila melanogaster are a biased subset that both maximizes meiotic drive and minimizes the frequency of lethal zygotes caused by this cytogenetic mechanism. Incorporating this form of selection into a population genetic model accurately predicts the shift in relative size, position, and linkage phase for rare inversions found in this species. The model and analysis presented here suggest that this weak form of female meiotic drive is an important process influencing the genomic distribution of rare inversion polymorphisms.