Macroevolution: Reproductive Isolating Mechanisms

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Reproductive isolating mechanisms

Prezygotic mechanisms

Postzygotic mechanisms

Hybrid sterility can be due to incompatibility between the genes of two species or to chromosomal differences that prevent normal meiosis. In some cases, species' chromosomes do not pair because of lack of homology. In other cases, pairing occurs but inviable gametes are formed when species differ by inversions and translocations. Inversions involve single pairs of homologous chromosomes, whereas translocations involve two pairs of homologous chromosomes.



Hybrids, like these zebroids (crosses between horses and zebras, shown
among horses) are often viable, but sterile.