Question

What is the difference between prezygotic and postzygotic reproduction barriers (reproductive isolating mechanisms, RIMs) between species (what is a zygote)? Give a real example of each.

Answer 1

Prezygotic isolation prevents the fertilization of eggseggs or in other words that prevent species from interbreeding with each other.

Postzygotic isolation prevents the formation of fertile offspring. It ensure the hybrid offspring are not selected for by natural selection.

Prezygotic mechanisms include: habitat isolation, mating seasons, "mechanical" isolation, gamete isolation and behavioral isolation.

Example of prezygotic isolation:

Snail Shell Coiling

• In some snail species, the direction of shell coiling
  x is controlled by a single (maternal effect) gene.

Example of post zygotic isolation

Drosophila spp.

• Despite their superficially similar appearance, D. melanogaster
  x and D. simulans have incompatible alleles
  x for nuclear pore proteins.
• Dysfunction of this vital gene results in inviable hybrids.

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