ABSTRACT
Recombination is the term originally used by geneticists to describe the outcome of crossing over between pairs of homologous chromosomes during meiosis. Crossing over results in daughter chromosomes that have different combinations of alleles compared with their parent chromosomes (Section 3.3). In the 1960s, models were proposed for the molecular events that underlie crossing over, and it was realized that a key part of molecular recombination is the breakage and subsequent rejoining of DNA molecules. Biologists now use recombination to refer to a variety of processes that involve the breakage and reunion of polynucleotides. These include the following:
Homologous recombination, also called general (or generalized) recombination, occurs between segments of DNA molecules that share extensive sequence homology. These segments might be present on different chromosomes or might be two parts of a single chromosome (Figure 17.1A). Homologous recombination is responsible for crossing over during meiosis and was initially studied in this context, but we now believe that its primary cellular role is in DNA repair. Two different types of recombination event. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315226828/f9ea4da9-cd6e-4b1e-8944-b57304f0c315/content/fig17_1.tif"/>
Site-specific recombination occurs between DNA molecules that have only short regions of sequence similarity, possibly just a few base pairs (Figure 17.1B). Site-specific recombination is responsible for the insertion of phage genomes, such as that of λ, into bacterial chromosomes.
