Expectations for the time scale and structure of allelic genealogies i
n finite populations are formed under three models of sporophytic self
-incompatibility. The models differ in the dominance interactions amon
g the alleles that determine the self-incompatibility phenotype: In th
e SSIcod model, alleles act codominantly in both pollen and style, in
the SSIdom model, alleles form a dominance hierarchy, and in SSIdomcod
, alleles are codominant in the style and show a dominance hierarchy i
n the pollen. Coalescence times of alleles rarely differ more than thr
eefold from those under gametophytic self-incompatibility, and transsp
ecific polymorphism is therefore expected to be equally common. The pr
eviously reported directional turnover process of alleles in the SSIdo
mcod model results in coalescence times lower and substitution rates h
igher than those in the other models. The SSIdom model assumes strong
asymmetries in allelic action, and the most recessive extant allele is
likely to be the most recent common ancestor. Despite these asymmetri
es, the expected shape of the allele genealogies does not deviate mark
edly from the shape of a neutral gene genealogy. The application of th
e results to sequence surveys of alleles, including interspecific comp
arisons, is discussed.