XB-IMG-157706
Xenbase Image ID: 157706
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Fig 5. Potential evolutionary scenarios forming X. mellotropicalis and X. epitropicalis karyotypes based on a common allotetraploid ancestor.
At least two evolutionary scenarios could form the allotetraploid species with the observed differences in the chromosomal locations of constitutive heterochromatic blocks. Scenario A indicates the translocation of a complete constitutive heterochromatic block from chromosome 9 to 2, and scenario B indicates the translocation of an incomplete constitutive heterochromatic block from chromosome 9 to 2. In (A), an ancestor of both allotetraploid species carried heterochromatic blocks on chromosomes 2a and 9b. In (B), genomic rearrangement produced a karyotype with the complete heterochromatic block on chromosomes 2a and 9b and a partial one on chromosome 9a. Sequence similarity of heterochromatic blocks from different chromosomes then facilitated a second incomplete (A) or complete (B) insertion of a heterochromatic block from chromosome 9b to 2a, which gave rise to the X. mellotropicalis karyotype. A residual hetrochromatic block on X. mellotropicalis chromosomes 9 was revealed by Zoo-FISH and is thus located either on chromosome 9b (A) or chromosome 9a (B). The formation of the X. epitropicalis karyotype from an allotetraploid ancestral species could have occurred via complete non-reciprocal recombination of a heterochromatic block between chromosomes 9a (or 9b) and 2a followed by an asymmetric pericentric inversion on chromosome 2a. Chromosome labelling “a”and “b”reflects the ancestral karyotypes (i.e. from which diploid ancestor a homoeologous pair is derived) and does not necessarily correspond with the chromosome names in the text which are based on the relative size of each homoeologous pair [23]. Chromosomal rearrangements between hypothetical or observed karyotypes of ancestral and extant species depicted out of the rectangular boxes are represented on haploid chromosomes.
https://doi.org/10.1371/journal.pone.0177087.g005 Image published in: Knytl M et al. (2017) © 2017 Knytl et al. This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution license Larger Image Printer Friendly View |