Table 1.

Definitions of terms

N	Number of organisms/duplicate genes in the population
λ	Number of initially incompatible nucleotide loci in a duplicate gene that must be changed to form the selectable, multiresidue feature
v	Point mutation rate per nucleotide per generation
ρ	Ratio of the number of possible mutations of the original duplicated gene that would produce a null allele to the number of possible mutations of the original duplicated gene that would yield a compatible residue. Neutral mutations, such as those that produce synonymous codons, are disregarded.
φ	Fraction of a particular nucleotide position that is in the incompatible state. (1 - φ) is the fraction in the compatible state.
t	Time, in generations
Tf	Time in generations to the first occurrence of a particular multiresidue, selectable features
Tfx	Time in generations to fixation in the population of a particular multiresidue, selectable feature
s	Selection coefficient