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| Modern Genetic Analysis Chapter 7. Gene Mutations The Molecular Basis of Mutation Figure 7-9. A simplified version of the Streisinger model for frameshift formation. (a) to (c) In DNA synthesis, the newly synthesized strand slips, looping out one or several bases. This loop is stabilized by the pairing afforded by the repetitive-sequence unit (the A bases, in this case). An addition of one base pair, A·T, will result at the next round of replication in this example. (d) to (f) If, instead of the newly synthesized strand, the template strand slips, then a deletion results. Here the repeating unit is a C·T dinucleotide. After slippage, a deletion of two base pairs (C·G and T·A) would result at the next round of replication.

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