TABLE 1

Summary of phenomena analyzed that contribute to asymmetric postzygotic isolation

Focal incompatibilitiesMaternal contributionsPaternal contributionsTypes of DMIs
X–autosomeaX, autosomesAutosomesUb and Bc
CytonuclearCytoplasmic organelles, nuclear genesNuclear genesU and B
Maternal effectsMaternal transcripts and proteins, nuclear genesNuclear genesU (and B)d
Triploid endospermDiploid genome (doubled haploid)Haploid genomeU (and B)e
Gametophytic–sporophyticfDiploid sporophyteHaploid gametophyteU
  • a Our analysis considers males in male-heterogametic species. In the text, we discuss the loci that make maternal (paternal) contributions to U DMIs as “female acting” (male acting).

  • b Unidirectional: These are the DMIs responsible for asymmetric postzygotic isolation.

  • c Bidirectional: These DMIs contribute equally to postzygotic isolation in both reciprocal crosses.

  • d Depending on the phenotype observed, B DMIs may or may not act simultaneously with U DMIs. For early embryo lethality, U DMIs may act alone. When considering embryo-to-adult viability, both act together.

  • e Depending on the phenotype observed, B DMIs may or may not act simultaneously with U DMIs. Triploid endosperm DMIs can be experimentally distinguished from zygotic DMIs; but if seed viability is assayed directly, both U and B DMIs will contribute.

  • f This includes pollen–style interactions.