Frame-shift mutations occur by strand slippage and mispairing during DNA replication. Mispairing usually occurs within runs of a particular nucleotide. Following strand slippage, the denatured strand can reanneal with one or more base pairs bulged out and the downstream nucleotides correctly base paired. If this mispaired strand if elongated by DNA polymerase, the mutation can be "fixed" in the new sequence. When this double-stranded DNA is subsequently replicated it will produce one daughter with the frame-shift mutation and one daughter with the wild-type sequence. This process can introduce either plus (the addition of 1 or 2 bp) or minus (the loss of 1 or 2 bp) frame-shift mutations as shown in the examples below.
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Last modified July 15, 2002