题目

下列关于质粒的叙述中，不正确的是（　　）                                          A．质粒的本质是DNA                                                                        B．质粒能自我复制                                                                             C．质粒是基因工程最常用的运载体                                                         D．质粒仅在于细菌体内                                                                           答案：解：A、质粒的本质是小型环状DNA，A正确；                                              B、质粒上具有复制原点，能自我复制，B正确；                                            C、质粒是基因工程最常用的运载体，C正确；                                               D、质粒主要来自于细菌，少数真核生物中也有质粒，D错误．                      故选：D．                                                                                         

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