465 14.2 Spontaneous mutation occur when an illegitimate nucleotide pair (say, A ? C) forms in DNA synthesis, leading to a base substitution. Also recall that earlier in the chapter we discussed that there are several forms of each base, called tautomers , and that the change of one tautomeric form to another can result in mispairing during DNA replication. Base insertion and deletion Although some errors in replication produce base-substitution mutations, other kinds of replication errors can lead to indel mutations —that is, insertions or deletions of one or more base pairs. When such mutations add or subtract a number of bases not divisible by three, they produce frameshift mutations in the protein-coding regions. The nucleotide sequence at frameshift mutation hot spots was determined in the lysozyme-encoding gene of phage T4. These mutations often occur at repeated bases. The prevailing model (Figure 14-21) proposes that indels arise when loops in single-stranded regions are stabilized by the “slipped mispairing” of repeated
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.