Selection at the haploid and diploid phases: cyclical variation.

This paper considers a deterministic model, where selection acts at both the diploid and haploid phases of development. The stability criteria for the maintenance of a protected polymorphism are derived. The implications of the model are examined through several examples, with emphasis on the comparison of these conditions to those of models that view selection as acting only at the diploid or haploid phases. It is found that the consideration of both phases broadens the conditions over such models.