Mutations211S - Mutation and Gene Alteration 1 Changing the...

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Mutation and Gene Alteration - 1 Changing the Genetic Message Although the processes of DNA replication and RNA transcription are remarkable in their fidelity, sometimes mistakes are made that alter the nucleotide sequence. Each chromosome has a distinct pattern, size and shape. Each gene is a precise sequence of DNA. Anything that affects the structure of a chromosome or a region of DNA, the nucleotide sequence of DNA, the number of chromosomes typical for a species, or that affects the ability of DNA to be transcribed accurately, is known as a mutation. More simply said, a mutation is a change in the nucleotide sequence of the DNA. Physical damage and chemical damage can also induce mutations, and are used by researchers to study mutations. Mutation is an important source of variation among individuals in populations, particularly those that reproduce asexually. The rate of mutation is highly variable, and depends in part of the ability of repair enzymes such as DNA polymerase and DNA ligase to fix mistakes, as mentioned earlier. Some genes mutate at much greater rates than others. Mutations can be passed from cell to cell by mitosis and from generation to generation. Mutations that occur in gamete formation (the germ-line cells) will be passed on to subsequent generations. Mutations in the somatic (or body cells) are not passed on to subsequent generations, but can have dramatic effects on the individual in whom they occur, particularly if they occur during development. We will begin our discussion with chromosome mutations. Phenotypic Effects of Mutation The phenotypic effects of mutation are also variable, and not surprisingly, are also defined. Mutations may enhance cell activity, be neutral or cause the cell to not function properly. A silent mutation is one that does not affect the function of the gene product, which is typically the protein for which the gene codes. Mutations may occur in non- coding portions of the DNA (DNA organization is discussed in our genome section) , or can be in a coded region that does not impact the gene product function. A mutation that results in loss of function will affect the gene product's function. Structural proteins or enzymes may not function. In diploid organisms, as discussed, a mutation may occur in one allele, but the alternative allele codes correctly and enough gene product is produced for the cell to function. Many of our recessive alleles are the result of loss of function mutations. A mutation that results in gain of function will enhance the gene product's function. Such mutations will typically be expressed as phenotypic dominant alleles. Conditional mutations affect the phenotypic expression only under certain conditions. Genes controlled by environmental conditions, such as temperature- sensitive genes can be the result of mutations that result in an unstable functional protein in certain environmental conditions.
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Mutation and Gene Alteration - 2 Phenotypic Effects of Mutations Mutation Categories
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Mutations211S - Mutation and Gene Alteration 1 Changing the...

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