Homologous and non-homologous recombination including transposition.

Krishan k jakhad

homologous or general recombination is very important since it is required for eukaryotic crossing-over during meiosis. various models e.g. Holliday/ heteroduplex model and double strand break models support this type of recombination between two homologous dsDNA molecules. sometimes very short similarly can help e.g. in site-specific recombination via Cre-LoxP system. In bacteria e.g. E.coli it is well reported and RecBCD complex (exonuclease V) has both nuclease and helicase activities. and responsible for integration of uptaken DNA via conjugation, transformation or transduction. RecA protein homologs in eukaryotic cells are Rad51 and Dmc1. Illegitimate recombination or nonhomologous recombination, is the process by which two unrelated double stranded segments of DNA are joined. This insertion of genetic material which is not meant to be adjacent tends to lead to genes being broken causing the protein which they encode to not be properly expressed. after transfection 3 events can be possible, 1. homologous recombination when DNA vector finds the correct gene inside embryonic stem cells integrate and replace it. 2. when correct gene is not found inside embryonic stem cells but it will randomly integrated into any part of chromosome, called non homologous recombination NHR...most common. 3. cells donot take up DNA at all.