A method for the production of biopolymers with modified properties wherein at least one cycle comprising the following steps is completed: (a) providing a population of single-stranded polynucleotide molecules, wherein individual polynucleotide molecules comprise homologous and heterologous sequence segments and wherein individual ones of said single-stranded polynucleotide molecules can form double-stranded polynucleotide molecules with other ones of said single-stranded polynucleotide molecules within said population; (b) forming double-stranded polynucleotide molecules from the population of single-stranded polynucleotide molecules provided according to step (a) comprising double-stranded polynucleotide molecules with different heterologous sequence segments; (c) partially and exonucleolytically degrading the single-strands of the double-stranded polynucleotide molecules produced according to step (b); and (d) temple-directed single-stand synthesizing the degraded ends of the partially degraded double strand produced according to step (c), wherein steps (c) and (d) may be carried out sequentially or contemporaneously.