The stationary frequency distribution and allelic dynamics in finite p
opulations are analyzed through stochastic simulations in three models
of single-locus, multi-allelic sporophytic self-incompatibility. The
models differ in the dominance relationships among alleles. In one mod
el, alleles act codominantly in both pollen and style (SSIcod), in the
second, alleles form a dominance hierarchy in pollen and style (SSIdo
m). In the third model, alleles interact codominantly in the style and
form a dominance hierarchy in the pollen (SSIdomcod). The SSIcod mode
l behaves similarly to the model of gametophytic self-incompatibility,
but the selection intensity is stronger. With dominance, dominant all
eles invade the population more easily than recessive alleles and have
a lower frequency at equilibrium. In the SSIdom model, recessive alle
les have both a higher allele frequency and higher expected life span.
In the SSIdomcod model, however, loss due to drift occurs more easily
for pollen-recessive than for pollen-dominant alleles, and therefore,
dominant alleles have a higher expected life span than the more reces
sive alleles. The process of allelic turnover in the SSIdomcod and SSI
dom models is closely approximated by a random walk on a dominance lad
der. Implications of the results for experimental studies of sporophyt
ic self-incompatibility in natural populations are discussed.