Genomic Differentiation and Its Effect on Gene Flow

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Abstract
Genomic differentiation occurs by structural rearrangements of chromosomes, by addition or deletion of DNA segments, and by mutations that affect the behavior of chromosomes or entire genomes. Depending on their size and other factors, structural changes can cause varying degrees of sterility in hybrids without regard to taxonomic level. Mitotic instability due to different kinds of mutations, structural rearrangements, and asynchronous behavior of heterochromatin can lead to hybrid weakness and segregational sterility in meiosis. Many structural changes of chromosomes are undoubtedly due to transposable elements. Hologenomic mutations, affecting entire genomes, may exert their effect in somatic tissue by causing certain kinds of mitotic instability such as centromere inactivation. However, some of these mutations may be expressed only in meiosis where they prevent normal chromosome pairing and/or failure of chiasma formation, so sterility in hybrids is caused by unbalanced gametes resulting from random disjunction of univalents.