Final answer:
The two general classes of genes found in the T-DNA region of the Ti plasmid are tumor-causing genes and desired DNA fragments.
Step-by-step explanation:
The two general classes of genes found in the T-DNA region of the Ti plasmid are tumor-causing genes and desired DNA fragments.
The natural transfer of DNA from Agrobacterium to a plant host allows the Ti plasmid to integrate into the plant cell's genome.
However, researchers manipulate the Ti plasmids to remove the tumor-causing genes and insert desired DNA fragments for transfer into the plant genome.