Abstract
A unified treatment of substitutional and mutational loads was presented assuming a steady flux of molecular mutations in a finite population. The case of genic selection for diploid populations (“no dominance”) was analysed in detail. The load is given by If(p) (formula 3) and several examples are illustrated in Fig. 2.
An important point which emerged from the analysis is that mutations with very small effects (having selection coefficients of the order of the reciprocal of the effective population number) can create considerable genetic load. This suggests that slightly detrimental mutations constitute a real threat to eventual extinction for a species having small population number. The mutational load as illustrated in Fig. 3 may be used to define the “cline” between neutral and deleterious mutations. The load depends on |Nes| rather than |s| alone. The importance of mutations with very small effects for variation and evolution of the species was discussed.
