Patent ID: 7208317

Claim:
A method for preparing a homozygous cellular library comprising: (a) providing a heterozygous cellular library comprising a plurality of isolated parent cells, wherein: (i) the plurality of isolated parent cells comprise a plurality of different genetic modifications; and (ii) each of the plurality of isolated parent cells comprises a marked chromosome pair comprising a first selectable marker at a first position distal to a first site-specific recombination site on a first chromosome of the marked chromosome pair, and a second selectable marker at a second position distal to a second site-specific recombination site of a second homologous chromosome of the marked chromosome pair, wherein the first and second selectable markers are both selected from the group consisting of dominant, negative selectable markers and recessive, positive selectable markers, thereby permitting recovery of the marked chromosome pair; and (iii) the plurality of isolated parent cells comprises a randomly mutagenized population of isolated cells; (b) providing a site-specific recombinase to the plurality of isolated parent cells, thereby inducing site-specific mitotic recombination in the plurality of isolated parent cells; (c) culturing the plurality of parent cells, whereby a population of daughter cells is produced; (d) replica plating the population of daughter cells; (e) selecting one replica of the population of daughter cells for each of the first and the second selectable markers; and (f) isolating at least one daughter cell comprising a homozygosed first chromosome of the marked chromosome pair and at least one daughter cell comprising a homozygosed second homologous chromosome of the marked chromosome pair, whereby a homozygous cellular library is prepared.