A conventional Dobzhansky-Muller model of speciation proposed that single-gene speciation would be difficult, because selection acts against a single mutation that causes reproductive isolation. On the other hand, it is believed that ecological speciation is promoted by a single speciation gene that contributes not only to reproductive isolation, but also to viability selection (pleiotropy). An excellent example is found in Southeast Asian land snails, in which left-right reversal of polarity by a single gene could have given rise to new species multiple times, as dextral and sinistral snails would rarely mate with each other. This might be facilitated by small population size and a maternal effect of handedness ('delayed inheritance', in which an individual's phenotype is determined by its mother's genotype), as well as a pleiotropic effect on anti-predator survival due to 'right-handed' snakes suggested by Hoso et al. (2010). Here we provide a theoretical framework to understand the single-gene speciation process affected by population size, the maternal effect, allele dominance, and pleiotropy. We show that the maternal effect and pleiotropy can promote speciation, and that the effects of allele dominance on fixation probability change according to the balance between pleiotropy and positive frequency-dependent selection due to reproductive isolation.