Deleterious mutations can accumulate in asexual haploid genomes through the 
process known as Muller's ratchet. This process has been described in the 
literature mostly for the case where all mutations are assumed to have the same 
effect on fitness. In the more realistic situation, deleterious mutations will 
affect fitness with a wide range of effects, from almost neutral to lethal. To 
elucidate the behavior of the ratchet in this more realistic case, simulations 
were carried out in a number of models, one where all mutations have the same 
effect on selection [one-dimensional (1D) model], one where the deleterious 
mutations can be divided into two groups with different selective effects 
[two-dimensional (2D) model], and finally one where the deleterious effects are 
distributed. The behavior of these models suggests that deleterious mutations 
can be classified into three different categories, such that the behavior of 
each can be described in a straightforward way. This makes it possible to 
predict the ratchet rate for an arbitrary distribution of fitness effects using 
the results for the well-studied 1D model with a single selection coefficient. 
The description was tested and shown to work well in simulations where selection 
coefficients are derived from an exponential distribution.