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| Modern Genetic Analysis Chapter 13. Transposable Genetic Elements Mechanism of Transposition Figure 13-13. Duplication of a short sequence of nucleotides in the recipient DNA is associated with the insertion of a transposable element; the two copies bracket the inserted element. Here the duplication that attends the insertion of IS1 is illustrated in a way that indicates how the duplication may come about. IS1 insertion causes a nine-nucleotide duplication. If the two strands of the recipient DNA are cleaved (arrow) at staggered sites that are nine nucleotides apart, as shown in (a), followed by insertion of IS1 between the resulting single-stranded ends, then the subsequent filling in of single strands on each side of the newly inserted element, indicated by red letters in (b), with the right complementary nucleotides could account for the duplicated sequences (boxes). (From S. N. Cohen and J. A. Shapiro, "Transposable Genetic Elements." Copyright © 1980 by Scientific American, Inc. All rights reserved.)

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