Article,
Substitution processes in molecular evolution. III. Deleterious alleles.
138 (3): 943--952 (1994)
Abstract
The substitution processes for various models of deleterious alleles are examined using computer
simulations and mathematical analyses. Most of the work focuses on the house-ofcards model,
which is
a popular model of deleterious allele evolution. The of
rate
substitution is shown to be a concave function
by a = 2Nu, where N is the population size and u is the standard
of the strength of selection as measured
deviation of fitness. For
a < 1, the house-ofcards model
is essentially a neutral model; for
a > 4, the model
ceases to evolve. The stagnation for large
a may be understood by appealing to the theory
of records. The
to a state where the vast majority of all mutations are deleterious, but precisely
house-of-cards model evolves
one-half of those mutations that fix are deleterious (the other half are advantageous). Thus, the model
is not a model of exclusively deleterious evolution as is frequently claimed. It is argued that there are no
biologically reasonable models of molecular evolution where the
vast majority of all substitutions are
deleterious. Other models examined include the exponential and gamma shift models, the Hartl-
Dykhuizen-Dean (HDD) model, and the optimum model. Of all those examined, only the optimum and
HDD models appear to be reasonable candidates for silent evolution. None
of the models are viewed as
good candidates for protein evolution, as none are both biologically reasonable and exhibit the variability
in substitutions commonly observed in protein sequence data.
Tags
- diffusion_approximation
- fixation_process
- genetic_draft
- point_processes
- population_genetics
- selection
- simulation
- time_series
