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Table 2 Ratio of R1 elements in the canonical 28S site, tandem arrays and non-28S locations

From: Origin of nascent lineages and the mechanisms used to prime second-strand DNA synthesis in the R1 and R2 retrotransposons of Drosophila

Species Fraction of rDNA units Tandem* Non-28S*
D. simulans 0.08 - +
D. sechellia 0.62 + +
D. melanogaster 0.11 - +
D. yakuba 0.11 - +
D. erecta 0.36 + -
D. ananassae R1A 0.17 ++ ++
D. ananassae R1B 0.13 +++ +++
D. pseudoobscura 0.40 +++ +++
D. persimilis 0.26 +++ ++
D. willistoni 0.10 + ++
D. mojavensis 0.68 + +
D. virilis 0.75 ++ +
D. grimshawi 0.20 + +
  1. *Plus signs indicate: +, less than 0.4 of those in 28S; ++, from 0.4 to 0.9 of those in 28S; +++, as many or more than those in the 28S; -, indicates absence. Unlike the tandem R1s in the ancestral group, the sequence between the many tandem-like, consecutive R1 elements in D. melanogaster is typical of that found in an insertion site rearrangement (ISR) junction. Unlike the highly variable ISR junctions found in the locus, the ISRs between these tandem-like R1s are the same. Thus, these elements are likely the result of amplification of an original unique event. All found upstream of R1B.