In the co- integrate vector system, maintenance of the recombinant T-DNA is dependent on recombination which can be enhanced byextensive homology between the two plasmids e.g.   Ti plasmid pGV3850 carrying a segment of the pBR322 backbone in its T-DNA.

Figure 5-4.4.2: Construction of a Co-integrate vector (foreign gene cloned into an appropriate plasmid is integrated with a disarmed Ti-plasmid through homologous recombination).

5-4.4.3. Binary vector

• Binary vector was developed by Hoekma et al (1983) and Bevan in (1984).
• It utilizes the trans- acting functions of the vir genes of the Ti-plasmid and can act on any T-DNA sequence present in the same cell.
• Binary vector contains transfer apparatus(the vir genes) and the disarmed T-DNA containing the transgene on separate plasmids.

5-4.4.3.1.Advantages of Binary vector

• Small size due to the absence of border sequences needed to define T-DNA region and vir region.
• Ease of manipulation