Haldane's Rule

Haldane's rule applies to the vast majority of heterogametic organisms examined. These include both male heterogametic and female heterogametic, and some dioecious plants such as Silene. It appears to be a general pattern associated with heterogamety.

Hybrid dysfunction (sterility and inviability) is a major form of postzygotic reproductive isolation, which occurs in early stages of speciation. The fact that evolution can produce such a similar pattern of isolation in a vast array of different organisms is striking. However, the actual mechanisms leading to this result in divergent taxa remains largely undefined. The basis by which the heterogametic sex becomes more susceptible to hybrid inferiority (sterility or inviability) has been a focus of theoretical and empirical explorations that have greatly enriched our understanding of sexual reproduction and speciation.