题目

After giving a talk at a high school, I was asked to pay a visit to a spe¬cial student. An illness had kept the boy home, but he had expressed an interest in meeting me. I was told it would mean a great deal to him, so I agreed.During the nine-mile drive to his home, I found out something about Matthew. He had muscular dystrophy (肌肉萎缩症). When he was born, the doctor told his parents that he would not live to five, and then they were told he would not make it to ten. Now he was thirteen. He wanted to meet me because I was a gold-medal power lifter, and I knew about overcoming2．科学家从某细菌中提取抗盐基因，转入烟草并培育成转基因抗盐烟草．如图是转基因抗盐烟草的培育过程，含目的基因的DNA和质粒上的箭头表示相关限制酶的酶切位点．请分析回答：（1）该技术定向改变了烟草的性状，这在可遗传变异的来源中属于基因重组．（2）①过程获得的抗盐基因可用PCR技术在体外进行大量扩增，该技术需用热稳定DNA聚合（Taq）酶；该技术的前提是要有一段已知目的基因的核苷酸序列，根据这一序列合成引物．（3）已知几种限制酶识别序列及其切割位点如表所示：限制酶BamHIHindIEcoRISmaI识别序列及其切割位点用图中的质粒和目的基因构建重组质粒，不能使用SmaⅠ切割，原因是SmaⅠ会破坏质粒的抗性基因、外源DNA中的目的基因．图中①、②过程为防止质粒和含目的基因的外源DNA片段自身环化，应选用限制酶BamHI和HindⅢ对外源DNA、质粒进行切割，再用DNA连接酶处理，形成重组质粒．（4）为筛选出已导入重组质粒的农杆菌，应在培养基中加M抗生素．（5）为确定转基因抗盐烟草是否培育成功，在个体水平上鉴定之前，常用放射性同位素标记的抗盐基因作探针进行分子杂交测试．