Gene mutation

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Genetic mutations A mutation is a herita table change of the genetic material Geneticists recognize three different levels at which mutation takes place. In gene mutation, , an allele of a gene changes, becoming a different allele. Because such a change takes place within a single gene and maps to one chromosomal locus ("point"), a gene mutation is sometimes called a point mutation. In chromosome mutations, , the structure of one or more chromosome is altered. Gene mutation is not necessarily a part of such a process; the effects of chromosome mutation are due more to the new arrangement of chromosomes and of the genes that they contain. Nevertheless, some chromosome mutations, in particular those proceeding from chromosome breaks, are accompanied by gene mutations caused by the disruption at the breakpoint. In genome mutations, , whole chromosomes, or even entire sets of chromosomes, change. Duplications of entire genomes in the course of evolution are particularly important as a mechanism resulting in sudden expansions in gene number Genetica per Scienze Naturali a.a. 08-09 prof S. Presciuttini
Basic terminology about gene mutation The ultimate source of genetic variation is gene mutation To consider change, we must have a fixed reference point, or standard. In genetics, the wild type provides the standard (the wild-type allele may be either the form found in nature or the form found in a standard laboratory stock). Any change away from the wild-type allele is called forward mutation; any change back to the wild-type allele is called reverse mutation. The non-wild-type allele of a gene is often called a mutation. . To use the same word for the process and the product may seem confusing, but in practice little confusion arises. Thus, we can speak of a dominant mutation or a recessive mutation. Consider, however, how arbitrary these definitions are; the wild type of today may have been a mutation in the evolutionary past, and vice versa. Another useful term is mutant. . A mutant organism or cell is one whose changed phenotype is attributable to the possession of a mutation. Sometimes the noun is left unstated; in this case, a mutant always means an individual or cell with a phenotype that shows that it bears a mutation. Two other useful terms are mutation event, , which is the actual occurrence of a mutation, and mutation frequency, , the proportion of mutations in a population of cells or individual organisms. Genetica per Scienze Naturali a.a. 08-09 prof S. Presciuttini
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Page 5 and 6: Germinal mutations Somatic mutation
Page 7 and 8: Point mutations: base substitutions
Page 9 and 10: Functional consequences of frameshi
Page 11 and 12: Mutations in non-coding regions No
Page 13 and 14: Errors in DNA replication Mispairi
Page 15: From mispairs to mutations (a) A gu

Gene mutation

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