| Summary: | 碩士 === 國立嘉義大學 === 農業生物技術研究所 === 94 === In addition to the normally important A chromosomes, the nucleus possesses some extra elements, called B chromosomes, found in many animal and plant cells. In plants, maize with B chromosomes has become the model system. Up to date, previous studies showed that the maize B chromosomes contain the dispersive specific CL-repeat sequences as well as other repeat elements such as CentC、CentA and CRM homologous to A chromosome DNA. Due to the highly homologues with A DNA, it is difficult to unveil the detailed structure of B chromosome by conventional methods. Recently a micro-dissection method was adopted to collect B chromosomes in the phase of pachytene and then two B-specific fragments about 13kb in size were cloned. In order to achieve larger pieces of B DNA, a large DNA cloning system such as bacterial artificial chromosomes (BAC) is required. This system has the followed advantages: large insert over 100 kb of DNA fragments, low rate of chimerism, stable BAC DNA in host cells, and easy DNA manipulation. In this study, BAC system was used to clone maize B chromosome DNA. In result, 4000 BAC clones were developed. After 3-dimensional PCR screening, three BAC clones carrying CL-repeat were identified. These clones contain the insert 80 to 95 kb fragments using CHEF analysis and host B DNA identified by southern blot analysis. In the future, these BAC clones would be decoded to provide some information of the structures of maize B chromosome useful for studies of its nature and evolution.
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