pyrimidine (or vice versa) is called a transversion . Single-base-pair additions or deletions (indels) produce frame-shift mutations. Certain human genes that contain tri-nucleotide repeats—especially those that are expressed in neural tissue—become mutated through the expan-sion of these repeats and can thus cause disease. The for-mation of monoamino acid repeats within the polypep-tides encoded by these genes is responsible for the mutant phenotypes. Mutations can be either spontaneous or induced by mutagenic radiation or chemicals. Spontaneous changes are generally a range of types. Mutagens often result in a specific type of change because of their chemical specificity. For example, some produce ex-clusively G · C : A · T transitions; others, exclu-sively frameshifts. Spontaneous base replacement can be from a type of chemical isomerization called tautomeric shift . Some chemicals exacerbate this type of change. Some mutagens alter the structure of a base, leading to new
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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.