| Life science is now facing an accelerated developmental moment profited from Human Genome Project and the analogous projects for model organisms. Compared to other placental mammals, cetacean researches are far droped behaind at molecular level, even cetaceans are the animals with the biggest changes of body-sizes, most world-wide distributions on the earth, and on the top niches in aquatic ecosystems. They have experienced a unique evolutionary process which is remarkably distinct to other mammals. In the present study, a BAC genomic DNA library for baiji, Lipotes vexillifer, was constructed, with some further preliminary investigations and discussions on genome evolution of placental mammals.The following goals were reached in this work:1) Using pBeloBAC11 and E. coli DH10B as cloning system, and lung tissue as source of genomic DNA, we had constructed a genomic DNA library for baiji. Each step had been optimized so that they can be used as references for other cetacean's library-construction.2) The library consists of 149,000 clones with an average insert size of 83kb. Among 175 random selected BAC clones, 2 are pseudo-positive. Based on the estimated haploid genome size of 3.6×109bp for baiji, the library represents about 3.4 equivalents of its haploid genome.3) PCR amplification for baiji's four known nuclear genes, the alpha lactalbumin gene, the interphotoreceptor retinoid-binding protein (IRBP) gene, the SINE flanking sequence Mago22 locus and the Mos (c-mos) gene partial sequence showed that about 2, 4, 2, 3 positive clones were got from the 21 super pools, respectively.
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