Table 1

Useful transformations for computing expectations and bounds for the rate of Muller's ratchet in diploids.

Genome type

Recessive

Co-dominant

Dominant

(h = 0)

(h = 0.5)

(h = 1)

(1) asexual haploid

(2) asexual diploid

Core-Genome-Model

Equal-Contribution-Model

Every-Allele-Needed-Model

(extreme forms are unrealistic)

(useful first order approximation)

(most unrealistic)

Stage 1

Stage 1

(MA is easy, may be harmless):

(MA is hard, may be impossible):

Stage 2

Stage 2

(MA is harder, may be impossible):

(MA is easier, may be still hard):

(3) asexual diploid with mitotic recombination

intermediate between genome type (2) and (4)

intermediate between genome type (2) and (4)

intermediate between genome type (2) and (4)

(4) automictic selfing diploid with free recombination

The table gives the variables in the exponent of , where N₀ is the number of individuals in the population that are in the 'best class' (has the highest fitness) in mutation-selection balance. Here we propose that Muller's ratchet in a given genome type can be approximated by using predictions for Muller's ratchet in a haploid asexual genome and applying the scaling given here. U_sdm = slightly deleterious mutation rate/haploid genome, s = homozygous selection coefficient, h = dominance coefficient, sh = heterozygous selection coefficient, where in this table positive s denote harmful mutations. The two stages for asexual diploids denote the fixation of the first and second deleterious mutation that can occur at a diploid locus. For individual stages, arrows indicate the change of U_sdm/s with increasing mutation accumulation (= MA). '<' or '>' indicate that mutation rates will remain below or above the indicated level, respectably.

Loewe and Lamatsch BMC Evolutionary Biology 2008 8:88   doi:10.1186/1471-2148-8-88