mutation

In biology, a change in the genes produced by a change in the DNA that makes up the hereditary material of all living organisms. It can be a change in a single gene or a change that affects sections of chromosomes. In the process of DNA replication, which takes place before any cell divides, the two halves of DNA separate and new halves are made. Because of specific base pairing, the inherited information is copied exactly. Despite this, rarely, a mistake occurs and the sequence of bases is altered. This changes the sequence of amino acids in a protein. This is mutation, the raw material of evolution. The consequences of mutation are varied. Due to the redundancy built into genetic code many mutations have no effect upon DNA functions. Genes describe how to make proteins. As a result of mutation a protein may not be produced, may be produced but act abnormally, or remain fully functional. Only a few mutations improve the organism's performance and are therefore favoured by natural selection. Mutation rates are increased by certain chemicals and by ionizing radiation.

Common mutations include the omission or insertion of a base (one of the chemical subunits of DNA); these are known as point mutations. Larger-scale mutations include removal of a whole segment of DNA or its inversion within the DNA strand. Not all mutations affect the organism, because there is a certain amount of redundancy in the genetic information. If a mutation is ‘translated’ from DNA into the protein that makes up the organism's structure, it may be in a non-functional part of the protein and thus have no detectable effect. This is known as a neutral mutation, and is of importance in molecular clock studies because such mutations tend to accumulate gradually as time passes. Some mutations do affect genes that control protein production or functional parts of protein, and most of these are lethal to the organism.

mutation

In music, an organ stop which produces a pitch other than the normal wavelength pitch (8 ft) or one related by octave (16 ft, 4 ft, 2 ft, or 1 ft). For example, a Quint stop (22/3 ft) produces a pitch an octave and a fifth higher than the depressed key (for example the C4 key sounds at G5). Other mutation stops sound higher by two octaves and a third, by two octaves and a fifth, or by two octaves and a flat seventh. They are not played alone, but with other stops which sound their proper notes.