Methods for in vitro recombination

A method for forming a mutagenized double-stranded polynucleotide from a template double-stranded polynucleotide, wherein the template double-stranded polynucleotide has been cleaved into double-stranded-random fragments of a desired size, comprising:

• a) adding to the resultant population of double-stranded random fragments one or more single or double-stranded oligonucleotide, wherein said oligonucleotides comprise an area of identity and an area of heterology to the double-stranded template polynucleotide;
• b) denaturing the resultant mixture of double-stranded random fragments and oligonucleotides into single-stranded fragments;
• c) incubating the resultant population of single-stranded fragments with a polymerase under conditions which result in the annealing of said single-stranded fragments at said areas of identity to form pairs of annealed fragments, said areas of identity being sufficient for one member of a pair to prime replication of the other thereby forming a mutagenized double-stranded polynucleotide;
• and
• d) repeating steps b) and c) for at least two further cycles, wherein the resultant mixture in step (b) of a further cycle includes the mutagenized double-stranded polynucleotide from step c) of the previous cycle, and the further cycle forms a further mutagenized double-stranded polynucleotide.