Chromosomal rearrangements

In T. miscellus genome rearrangements via intergenomic translocations were common; 76% of the plants showed evidence of at least one translocation. The two largest chromosomes (groups A and B) showed the highest incidence of translocations. Across all T. miscellus plants at least six different translocation breakpoint positions were observed along the A group chromosomes. In one T. miscellus population in Spokane (WA), an A chromosome intergenomic translocation appeared close to fixation, being homozygous in eight of the 10 individuals analyzed. Individuals from six populations also appear to have undergone reciprocal translocations on the B group chromosomes but they mostly occur at a similar position, near the end of the long arm (Chester et al., 2012).

In T. mirus, changes in chromosome structure paralleled what was seen in T. miscellus (Chester et al., 2015). Repeated independent intergenomic translocations occurred at three distal regions in the genome of T. mirus (A long arm, C short arm and C long arm). Multiple T. miscellus populations also had intergenomic translocations in similar regions (Chester et al., 2012). Application of FISH to T. mirus, as for T. miscellus (Chester et al., 2013), showed that repetitive DNA was also lost from these regions in some individuals. Although translocations were common in T. mirus, most individuals typically showed only one or two translocations differentiating them from a non-rearranged karyotype. This observation also applies to the T. miscellus populations that were analyzed (Chester et al., 2012).

Application of GISH to synthetic lines of both allotetraploids revealed that chromosomal rearrangements as well as aneuploidy developed quickly in synthetics and resembled that of naturally occurring T. mirus and T. miscellus by generation S₄ (Spoelhof et al., 2017).