Interspecific hybridization represents one of the main mechanisms of plant speciation. Merging of two genomes from different subspecies, species, or even genera is frequently accompanied by whole-genome duplication (WGD). Besides its evolutionary role, interspecific hybridization has also been successfully implemented in multiple breeding programs. Interspecific hybrids combine agronomic traits of two crop species or can be used to introgress specific loci of interests, such as those for resistance against abiotic or biotic stresses. The genomes of newly established interspecific hybrids (both allopolyploids and homoploids) undergo dramatic changes, including chromosome rearrangements, amplifications of tandem repeats, activation of mobile repetitive elements, and gene expression modifications. To ensure genome stability and proper transmission of chromosomes from both parental genomes into subsequent generations, allopolyploids often evolve mechanisms regulating chromosome pairing. Such regulatory systems allow only pairing of homologous chromosomes and hamper pairing of homoeologs. Despite such regulatory systems, several hybrid examples with frequent homoeologous chromosome pairing have been reported. These reports open a way for the replacement of one parental genome by the other. In this review, we provide an overview of the current knowledge of genomic changes in interspecific homoploid and allopolyploid hybrids, with strictly homologous pairing and with relaxed pairing of homoeologs.

Department of Plant Developmental Genetics Institute of Biophysics of the Czech Academy of Sciences Brno Czechia

Institute of Experimental Botany Czech Academy of Sciences Centre of the Region Hana for Biotechnological and Agricultural Research Olomouc Czechia

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Proportion of parental genomes in hybrids Allium cepa × A. roylei determines which one becomes dominant

Uniparental expression of ribosomal RNA in ×Festulolium grasses: a link between the genome and nucleolar dominance

Genome Dominance in Allium Hybrids (A. cepa × A. roylei)

Reciprocal allopolyploid grasses (Festuca × Lolium) display stable patterns of genome dominance