Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/21601
標題: Structural Variations of the B Chromosome in Maize
玉米B染色體的構造變異
作者: 林耀斌
Lin, Yaw-bin
關鍵字: 染色體的變異
chromosome mutation
B染色體
B-A易位染色體
B chromosome
B-A translocation
出版社: 分子生物學研究所
摘要: 本論文旨在研究B染色體兩種不同型式的構造變異:第一種是發生在B染色體,第二種是B-A易位染色體(translocation)的B部分。完整的B染色體在粗絲期(pachytene)帶有常染色質(euchromatin)的短臂,接上被染色體球(knob)所包圍的中節區域,再連著長臂(包含近端常染色質區、四段末端異染色質區─ DH1至DH4、與末端常染色質區)。而第一種變異的B染色體,其長臂的近端常染色質區缺失,但仍帶有末端異染色質區。第二種變異是發生在TB-6Lc,該易位染色體包含6-B及B-6染色體,其中正常的6-B染色體帶有第六條染色體的短臂、中節、一小部分長臂、以及B染色體的後二段末端異染色質區(DH3及DH4)和末端常染色質區;變異的6-B染色體則失去DH3及DH4區域。這兩種B 染色體構造的變異結果與序列同源性分析相符合,即變異和正常的B染色體帶有一個DH4的序列,變異的6-B染色體則否。 玉米的B染色體在第二次花粉有絲分裂時會發生不分離現象(nondisjunction),該現象受到三個B區域(nondisjunction factors)所調控,其中第一調控區位於末端常染色質區、第二調控區是在近端常染色質區、第三調控區則座落在短臂。這三個調控區需同時存在一個細胞中,B染色體才會發生不分離現象。正常B 染色體帶有這三個調控區,其不分離率為84.91 %;但是變異的B染色體沒有不分離現象,此特性加上它的構造缺失近端常染色質區,表示此染色體至少不帶第二調控區。而正常的6-B染色體帶有第一調控區,B-6染色體則帶有另外兩個調控區。在6-B染色體存在下能誘導B-6染色體發生95.86 %的不分離頻率;而變異的6-B染色體也保有此能力,其發生頻率為96.45 %,表示此染色體仍帶有第一調控區。
This thesis is aimed to study two derivatives of the B chromosome: one derived from the B chromosome, and the other derived from the B parts of TB-6Lc translocation. An intact B chromosome comprises a euchromatic short arm, a centromere-carrying knob, and a long arm, which is composed of a proximal euchromatic (PE), four distal heterochromatic (DH1 to DH4), and a distal euchromatic region (DE). The first derivative deletes the PE of the B chromosome, but retains the DH regions. The second derivative is associated with the TB-6Lc translocation, which includes a 6-B and a B-6 chromosome. The 6-B chromosome carries DH3, DH4, and DE regions of the B chromosome. The 6-B derivative is deficient of DH3 and DH4. Both structural deficiencies are consistent with the homology analysis of a DH4 sequence, which is present in the first derivative but absent in the second. The B chromosome undergoes nondisjunction at the second pollen mitosis, which is conditioned by three factors. Factor-1 is located in DE, factor-2 in PE, and factor-3 in the B short arm. These three factors need to be present in the same cell in order for the B chromosome to nondisjoin. The nondisjunction frequency of a normal B chromosome is 84.91 %. But the B derivative fails to undergo nondisjunction, indicating the deletion of factor-2. A normal 6-B chromosome contains factor-1, and the B-6 chromosome carries factor-2 and factor-3. The 6-B chromosome provoked nondisjunction of the B-6 chromosome at a frequency of 95.86 %. The 6-B derivative retains this ability and causes a 96.45 % nondisjunction frequency, indicating the presence of factor-1.
URI: http://hdl.handle.net/11455/21601
Appears in Collections:分子生物學研究所

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