TABLE 3

Factors expected to contribute to (+), oppose (−), or have no effect on (0) Haldane's rule

Male heterogameticFemale heterogametic
FactorsInviabilitySterilityInviabilitySterility
Dominance++++
Faster-male evolution0+0
Y-associated incompatibilities0+0+
Maternal-zygotic incompatibilities0+0
  • The Y has no essential somatic function. It is not expected, therefore, to play a role in hybrid inviability (hence the “0” entries). Similarly, maternal gene effects cease early in development. They are not expected, therefore, to play a regular role in a “late” phenotype like adult fertility (hence the “0” entries).