Disclosed herein is an efficient method of generating a library of variants of a sequence of interest, such as may be used in directed evolution. In one embodiment, the method includes an amplification reaction, e.g., error-prone PCR, to generate double-stranded DNA (dsDNA) variants of a sequence of interest, after which one strand of the dsDNA variants may be selectively degraded to produce single-stranded DNA (ssDNA) variants. The ssDNA variants may be hybridized to ssDNA intermediaries, e.g., uracilated circular ssDNA intermediaries, to form heteroduplex DNA, which may be transformed into cells, such as E. coli cells, yielding a library of variants. This method eliminates the inefficient sub-cloning steps and the need for costly primer sets required by many prior methods.