Which of the following way/s above you do frequently? why?

A mutation (Section 14.1) is a change in the nucleotide sequence of a short region of a genome (Figure 14.1A). Many mutations are point mutations that replace one nucleotide with another; others involve insertion or deletion of one or a few nucleotides. Mutations result either from errors in DNA replication or from the damaging effects of mutagens, such as chemicals and radiation, which react with DNA and change the structures of individual nucleotides. All cells possess DNA-repair enzymes that attempt to minimize the number of mutations that occur (Section 14.2). These enzymes work in two ways. Some are pre-replicative and search the DNA for nucleotides with unusual structures, these being replaced before replication occurs; others are post-replicative and check newly synthesized DNA for errors, correcting any errors that they find (Figure 14.1B). A possible definition of mutation is therefore a deficiency in DNA repair.

Recombination (Section 14.3) results in a restructuring of part of a genome, for example by exchange of segments of homologous chromosomes during meiosis or by transposition of a mobile element from one position to another within a chromosome or between chromosomes (Figure 14.1C). Various other events that we have studied, including mating-type switching in yeast (see Figure 12.13) and construction of immunoglobulin genes (see Figure 12.15), are also the results of recombination. Recombination is a cellular process which, like other cellular processes involving DNA (e.g. transcription and replication), is carried out and regulated by enzymes and other proteins.

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