The Molecular Basis of Recombination

Recombination is the exchange of genetic information between DNA molecules; when the exchange is between homologous DNA molecules, it is called homologous recombination. This process takes place in crossing over, in which homologous regions of chromosomes are exchanged (see Figure 2.17) and genes are shuffled into new combinations. Recombination is an extremely important genetic process because it increases genetic variation. Rates of recombination provide important information about linkage relations among genes, which is used to create genetic maps (see Figures 7.12 through 7.14). Recombination is also essen tial for some types of DNA repair (as will be discussed in Chapter 17).

Homologous recombination is a remarkable process: a nucleotide strand of one chromosome aligns precisely with a nucleotide strand of the homologous chromosome, breaks arise in corresponding regions of different DNA molecules, parts of the molecules precisely change place, and then the pieces are correctly joined. In this complicated series of events, no genetic information is lost or gained. Although the precise

Chromosomes cross over

Exchange of segments

DNA synthesis

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