Fig. 1

Schema of the comparisons made among the cotton species and various ploidies. a AA and DD = ancestral diploid genome types. AD = diploid hybrid. AADD = allotetraploid. Dotted line shows comparisons made in Song et al. [2]. b Genes shown as blue boxes on vertical lines for AA and DD diploids and an AADD tetraploid. Green circles illustrate DNA methylation showing from top to bottom: no methylation in diploids and no methylation in allotetraploid; transfer of methylation from the A genome of a diploid to the D subgenome in an allotetraploid; and finally, the formation of a novel epiallele that is not observed in the two ancestral diploids