Interpopulation gene flow in plants is mediated by a combination of po
llen and seed dispersal. The effectiveness of pollen and seeds in brin
ging about gene flow depends upon the mode of inheritance of the genet
ic marker. For nuclear and paternally inherited markers, gene flow occ
urs in both pollen and seed. For maternally inherited markers, genes a
re only dispersed in seeds. As a result, levels of population differen
tiation under drift-migration equilibrium are expected to differ for m
arkers with contrasting modes of inheritance, and the extent of such d
ifferences should be related to the relative levels of pollen and seed
migration among populations. A model is developed that relates expect
ed values of population differentiation (F-st) for nuclear, paternally
and maternally inherited markers, to pollen and seed migration rates.
The model is used to estimate the relative rates of seed and pollen f
low in six species of plants where F-st values are available for both
nuclear and maternally inherited markers. Estimates of (pollen flow/se
ed flow) range from four in wild barley to 200 in oaks, and this patte
rn of variation is consistent with the reproductive characteristics of
the species concerned.