Final answer:
Ti-plasmids of Agrobacterium tumefaciens are commonly used as vectors for gene transfer in crop plants, facilitating the creation of transgenic plants without the tumor-inducing effects.
Step-by-step explanation:
The vector commonly used in the transfer of genes in a crop plant is the Ti-plasmids of Agrobacterium tumefaciens. These plasmids act as shuttle vectors for incorporating genes into plants. The Ti-plasmids in nature cause plants to develop tumors but have been engineered by scientists to remove the tumor-causing genes. Instead, they are used to insert desired DNA fragments into the plant genome to create transgenic plants. This process exploits the natural mechanism of gene transfer from Agrobacterium to the plant host.