Vectors for Cloning in Plants and Animals (Ti Plasmid, Retrovirus)
Biology · Biotechnology: Principles and Processes · NEET
For cloning genes into plants and animals we borrow tools from natural pathogens. The Ti (Tumor inducing) plasmid of Agrobacterium tumefaciens is "disarmed" (made non-pathogenic) and used to carry our gene into plant cells, while disarmed retroviruses carry genes into animal cells. Memory hook: "Plants get Ti, animals get Retro" — the pathogen that once caused tumors now delivers useful genes.
Ti plasmid of Agrobacterium delivers genes into plant cells (via T-DNA); disarmed retroviruses deliver genes into animal cells. Both are once-harmful pathogens now made non-pathogenic.
Your doubts, answered
Is the Ti plasmid used for plants or animals? I keep mixing it up.
The Ti plasmid is used for PLANTS. It comes from Agrobacterium tumefaciens, a bacterium that naturally infects dicot plants. For ANIMAL cells (including human cells), the vector is a disarmed retrovirus. Simple rule: Ti plasmid -> plants; retrovirus -> animals.
What does 'Ti' stand for, and why does the name matter?
Ti stands for Tumor inducing. In nature the Ti plasmid makes normal plant cells grow into a tumor and forces them to make food for the bacterium. NEET has directly asked the full form (NEET 2024), so remember: Ti = Tumor inducing plasmid, NOT tumor inhibiting or independent.
What does 'disarmed' mean for these vectors?
Disarmed means the disease-causing (pathogenic) genes have been removed, so the vector can no longer cause tumors or cancer. It still keeps the machinery to enter the host cell and deliver DNA. So the modified Ti plasmid is no longer harmful to plants, and disarmed retroviruses no longer make animal cells cancerous — they only carry the gene we want.
Which vector is used to put a gene into human lymphocytes?
A retrovirus. Human lymphocytes are animal cells, and disarmed retroviruses are the vectors used to deliver genes into animal cells. This was the exact answer NEET wanted in 2018 — not Ti plasmid, not lambda phage, not pBR322.
What is T-DNA and how is it different from the Ti plasmid?
T-DNA (transfer DNA) is the specific piece of DNA that Agrobacterium delivers into the plant cell. The Ti plasmid is the whole circular plasmid that carries this T-DNA. In natural infection, the T-DNA transforms the plant cell into a tumor; in the lab, we replace the tumor-causing part with our gene of interest.
Can Agrobacterium tumefaciens transfer genes into animal cells too?
No. Agrobacterium (via Ti plasmid / T-DNA) transfers genes into PLANT (eukaryotic) cells, not animal cells. A common NEET trap statement says it works in 'both prokaryotic and eukaryotic hosts' — that statement is INCORRECT (NEET 2023).
⚠️ The NEET trap ✗ Ti plasmid and retrovirus can both be used to clone genes into any cell — plant or animal. ✓ Ti plasmid delivers genes into PLANT cells only; disarmed retrovirus delivers genes into ANIMAL cells only. Each pathogen keeps its natural host range. 🧠 Match the pathogen to its natural victim: the plant tumor bug (Agrobacterium/Ti) stays with plants, the animal cancer virus (retrovirus) stays with animals.
Real NEET questions
NEET 2018
Which of the following is commonly used as a vector for introducing a DNA fragment in human lymphocytes?
A · λ phage
B · Ti plasmid
C · Retrovirus ✓
D · pBR322
Solution: Human lymphocytes are animal cells. Disarmed retroviruses are the vectors used to deliver genes into animal cells. Ti plasmid is for plants; λ phage and pBR322 are bacterial cloning vectors.
NEET 2024
The 'Ti plasmid' of Agrobacterium tumefaciens stands for
A · Tumor independent plasmid
B · Tumor inducing plasmid ✓
C · Temperature independent plasmid
D · Tumour inhibiting plasmid
Solution: Ti = Tumor inducing plasmid. In nature it delivers T-DNA that induces tumours in dicot plants; when disarmed it becomes a non-pathogenic cloning vector for plants.
NEET 2023
Which of the following statement is incorrect about Agrobacterium tumefaciens?
A · It transforms normal plant cells into tumorous cells.
B · It delivers 'T-DNA' into plant cell.
C · It is used to deliver gene of interest in both prokaryotic as well as eukaryotic host cells. ✓
D · 'Ti' plasmid from Agrobacterium tumefaciens used for gene transfer is not pathogenic to plant cells.
Solution: Agrobacterium (via Ti plasmid/T-DNA) delivers genes into plant (eukaryotic) cells, not into 'both prokaryotic and eukaryotic' hosts. So statement (C) is the incorrect one.
Solved Biotechnology: Principles and Processes NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Are Ti plasmid and retrovirus natural or engineered vectors?
Both start as natural pathogens (Agrobacterium's Ti plasmid causes plant tumors; retroviruses cause animal cancers). Scientists engineer them by removing the harmful genes ('disarming') so they safely deliver the gene of interest.
Why do we use pathogens as vectors at all?
Because these pathogens are already experts at forcing eukaryotic cells to take up and express foreign DNA — a skill bacteria and viruses evolved over ages. We simply redirect that ability to carry our useful genes instead of disease genes.
Is Ti plasmid a cloning vector like pBR322?
Yes, both are cloning vectors, but for different hosts. pBR322 is a bacterial plasmid vector; the disarmed Ti plasmid is a plant vector. NCERT groups Ti plasmid and retrovirus separately as 'vectors for cloning genes in plants and animals.'
What is the difference between transformation here and normal bacterial transformation?
Here 'transform' has two meanings. Naturally, Agrobacterium transforms a plant cell into a tumor cell. In cloning, 'transformation' simply means the host cell takes up the recombinant DNA. NCERT uses the pathogen's transforming ability as the delivery mechanism.
