Selection is multiplicative across loci, so that a genotype with i heterozygous recessive lethal mutations has a relative fitness of [Mathematical Expression Omitted], where h is the dominance coefficient and the mean fitness in the population.
Identity disequilibrium, measured as the variance to mean ratio of number of recessive lethal mutations in adult plants, generally increases with increasing asexuality, both with respect to relative and absolute selfing rate [ILLUSTRATION FOR FIGURE 1C OMITTED].
Because populations of these species consist of several large clones, their genomic lethal mutation rates per sexual generation may be much higher.
We show that a large average number of recessive lethals (or lethal equivalents) per plant, maintained by a high genomic lethal mutation rate, interferes with the purging of lethals by self-fertilization.
In designing such experiments, it is most straightforward to use microorganisms, given their short generation time and readily available conditional lethal mutations
. For example, auxotroph mutants are easy to maintain and observe on selective media and are strongly selected against on restrictive media (Welden & Hossler, 2003; Krist & Showsh, 2007).
A number of theoretical models have indicated that the genetic load due to recessive lethal mutations
is rapidly purged from a population following even a small amount of inbreeding, whereas that component of the load due to mildly deleterious mutations or to polygenic mutations is difficult to purge (Lande and Schemske 1985; Charlesworth and Charlesworth 1987; Charlesworth et al.
Although lethal mutations have been documented for Mimulus (Kiang and Libby 1972; Willis 1992), they likely do not play an important role in inbreeding depression.
If lethal mutations are expressed earlier than less deleterious mutations, then the late expression of inbreeding depression in Mimulus suggests that mildly deleterious recessive mutations are the main cause of inbreeding depression in Mimulus.
Neutral mutations have no influence on the probability of extinction, whereas lethal mutations are eliminated in a single generation and have no cumulative effect.
Simulations were done for a range of !s.sub.1^ in the first deme, keeping !s.sub.2^ = 1 (lethal mutations) constant in the second.