Figure 3. Unusual long palindromic GI, GII and GIII sequences and their potential evolution from REP doublets found in the SBW25 genome. (A) Shown are all four long palindromic GI, GII and GIII sequences together with their frequency found in the SBW25 genome. Note that two configurations are found for GI sequences and only one for both GII and GIII sequences. (B) Shows how long palindromic REP singlets could arise from REP doublets through the excision of the central sequence. Hence, REP doublets found in AA-TT orientation would produce a-palindrome-ac REPs (left) and REP doublets found in TT-AA orientation bc-palindrome-b REPs (right).