Single burst study of rec and red mediated recombination in bacteriophage lambda

Single bursts from three point crosses of bacteriophage λ were analyzed for recombination of markers several thousand nucleotide pairs apart. Single recombination, mediated by the rec system of Escherichia coli, is usually reciprocal. Double recombinants are also significantly correlated in single bursts, although the correlation is weaker than for reciprocal singles. Reciprocity is not found in crosses mediated by the λ red system. With respect to certain other parameters of recombination, the two systems appear to be alike. Double recombinants usually result from one event, not from two independent single recombinations, and their average clone size is about half that of single recombinants. The results are discussed in terms of current molecular models of recombination.