[Three-dimensional PCR-based screening of Chinese fine wool merino sheep BAC library]

For rapid screening, we constructed two levels pools (primary and secondary pools) of the bacterial artificial chromosome (BAC) library of Chinese fine wool merino sheep. The primary pools were based on the individual 384-well microtiter plate and were prepared with a three-dimensional pooling scheme. Three dimension (plate, row and column) pools were made for each. The secondary pools were based on the entire BAC library. We developed a PCR based strategy to identify positive BACs from sheep BAC library. First, we analyzed secondary pools DNAs, according to the result, we analyzed correlative primary pools. It was one-step screening (66 PCR reactions) that we could screen a single positive clone from 74 000 BACs by our method, or three-step screening (less than 100 PCR reactions) could screen more clones. By one-step screening (66 PCR reactions), we screened successfully a positive clone 373D13 with polymorphism marker BF94-1.