Genomic Asymmetry for Morphology in Allopolyploids Within and out of <i>Brassica</i>

Abstract

The genomic asymmetry in the nonrandom retention and expression of controlling genes for some traits from one parental diploid is obvious in some natural and synthetic allopolyploids, and has the evolutionary implications. Here we review the genomic asymmetry for the morphological performance in three cultivated <i>Brassica</i> allotetraploids and some intergeneric allopolyploids within <i>Brassicaceae</i> species. For the phenotypic biases of <i>Brassica</i> allotetraploids, <i>Brassica oleracea</i> (genomes CC) is dominant over <i>B. nigra</i> (BB) and <i>B. rapa</i> (AA) in <i>B. carinata</i> (CCBB) and <i>B. napus</i> (CCAA), respectively, and <i>B. nigra</i> is dominant over <i>B. rapa</i> in <i>B. juncea</i> (BBAA), showing the C>B>A dominance hierarchy. However, the morphology of several <i>Brassica</i> species including <i>B. oleracea</i> at top dominance is largely recessive in their intergeneric hybrids and allopolyploids with other crucifers, such as <i>Raphanus sativus</i>, <i>Orychophragmus violaceus</i>. The morphology of <i>Arabidopsis thaliana </i>is also recessive in its two allotetraploids. Among the dominant features, the leaf serration is expressed consistently in these intergeneric and <i>Arabidopsis</i> allopolyploids. The phenotype expression of the recessive diploid is subject to the euploidy or aneuploidy state of its genome, and the dominant traits are still mostly expressed in the aneuploidy state of their genome. The morphological biases in these allopolyploids are discussed in the contexts of the genomic structure and interplay.