Practice question · Sort into groups
Sort each isolating mechanism by when it acts.
Groups: Prezygotic, before fertilisation · Postzygotic, after fertilisation
- Gametes are chemically incompatible
- The two species breed in different seasons
- Courtship displays are not recognised across species
- Hybrid offspring are sterile, like the mule
- Hybrid offspring die before maturity
Hints
- The dividing line is whether a zygote is ever formed.
- Anything that prevents mating or fertilisation is prezygotic.
Show the answer
Prezygotic, before fertilisation: The two species breed in different seasons, Courtship displays are not recognised across species, Gametes are chemically incompatible
Postzygotic, after fertilisation: Hybrid offspring die before maturity, Hybrid offspring are sterile, like the mule
Why
Prezygotic barriers stop a zygote forming; postzygotic ones act on the hybrid. Selection generally favours prezygotic barriers, because a wasted mating is cheaper than a wasted offspring.
Practise Speciation and the Origin of Diversity
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