The population genetics of the B-chromosome polymorphism of Myrmeleotettix maculatus (Orthoptera: Acrididae)

A simple difference equation model of the dynamics of the B-chromosome of Myrmeleotettix maculatus is developed, validated with field data, and analysed. The maintenance of the B in a population is due to a frequency-dependent balance between a net meiotic drive and strong selection against karyotypes containing 2 B's. This equilibrium will be subject to substantial fluctuations even in moderately large populations. In the long run a B is likely to be maintained in a population despite the selection of suppressor genes, which will tend to remain polymorphic in the population. These qualitative conclusions are likely to apply to many B-chromosome systems.