Few estimates exist for the total genomic mutation rate to recessive lethal alleles. In Drosophila melanogaster about n = 5000 loci produce recessive lethal mutations with an average mutation rate per generation of [Mathematical Expression Omitted] (Simmons and Crow 1977), giving a (diploid) genomic lethal mutation rate of U = 0.02 per generation.
The first model is based on the approximation of identity equilibrium among mature plants, entailing a Poisson distribution of recessive lethal alleles at a large (but finite) number of unlinked loci.
This model assumes a finite number of unlinked loci mutating to (nearly) recessive lethal alleles. It accounts for identity disequilibrium produced among selfed and outcrossed zygotes each generation, but assumes identity equilibrium among mature plants.
Because homozygous lethal alleles at any locus generally are kept rare by selection, 2H [much greater than] 1, the variance closely approximates the mean, and the distribution of number of lethals per plant is nearly Poisson.
We assume that the number of loci mutating to recessive lethal alleles is quite large, such that any one locus contributes a very small fraction of the total inbreeding depression in the population.
Selective interference and identity disequilibrium among loci can be fully incorporated in a model that describes the evolution of the distribution of number of heterozygous lethal alleles per mature plant in a population.