Sex ratio equilibrium under partial sib mating

A general equation for equilibrium sex allocation is provided which models asymmetries between son and daughter in the costs of offspring production, the genetic relatedness to the controlling genotype and the amount of competition for mating opportunities and reproductive resources. A genetic proof is given which is valid for diploid and haplodiploid systems with a variety of modes of sex allocation control, provided sib mating is the only source of inbreeding. By way of example, some variations of Hamilton's (1967) model are discussed.