Question and Answer:

Question 1.
Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because

1. bacteria are resistant to the toxin
2. toxin is immature;
3. toxin is inactive;
4. bacteria encloses toxin in a special sac.

Answer:
(c) toxin is inactive
Explanation:
Bt toxin produced by Bacillus thuringiensis is present in the form of inactive protoxins.
These protoxins become active only inside the alkaline gut of insects, where they get solubilized and converted into active toxins.
Since the toxin remains inactive inside the bacteria, it does not harm the bacteria itself.

Question 2.
What are transgenic bacteria? Illustrate using any one example.
Answer:

Transgenic bacteria are genetically modified bacteria that carry and express foreign genes introduced into them through recombinant DNA technology.

Example:
E. coli has been made transgenic to produce human insulin.
Scientists introduced two separate DNA sequences coding for the A-chain and B-chain of human insulin into plasmids of E. coli.
These transgenic bacteria then produced the insulin chains, which were later combined to form functional human insulin used for treating diabetes.

Question 3.
Compare and contrast the advantages and disadvantages of production of genetically modified crops.
Answer:

Advantages of GM crops:

• Genetic modification makes crops more tolerant to abiotic stresses such as cold, drought, heat, and salinity.
• Viral resistance can be introduced into plants.
• Post-harvest losses and over-ripening can be reduced.
  Example: Flavr Savr tomato.
• Nutritional quality of food can be enhanced.
  Example: Golden rice enriched with Vitamin A.
• Reduced reliance on chemical pesticides, as some GM crops (e.g., Bt crops) are pest-resistant.

Disadvantages of GM crops:

• Transgenes may escape into wild relatives, affecting native species and ecosystem balance.
• Bt toxin expressed in pollen may potentially harm non-target pollinators like honeybees.
• Weeds may develop resistance, leading to “superweeds.”
• Products of transgenes may sometimes cause allergic reactions or may be toxic to some individuals.
• Large-scale use of GM crops may cause ecological disturbances and loss of biodiversity.

Question 4.
What are Cry proteins? Name an organism that produce it. How has man exploited this protein to his benefit?
Answer:

Cry proteins are insecticidal proteins (Bt toxins) that kill lepidopteran insects and their larvae. These proteins are produced by the bacterium Bacillus thuringiensis.

Exploitation by humans:
The cry gene that encodes the Bt toxin has been isolated from Bacillus thuringiensis and introduced into the cotton plant genome using Agrobacterium Ti plasmid (T-DNA) as a vector.
The resulting GM crop, Bt cotton, produces the toxin in its tissues and becomes naturally resistant to insect pests, reducing the need for chemical pesticides.

Question 5
What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.
Answer:

• Gene therapy is a collection of methods that allow the correction of a diagnosed gene defect in a child or embryo. In this technique, normal functional genes are inserted into a person’s cells or tissues to treat a hereditary disorder.
  Gene therapy is currently being tried for conditions like sickle cell anaemia and Severe Combined Immuno Deficiency (SCID).
• In some children, ADA (Adenosine Deaminase) deficiency can be treated by bone marrow transplantation. In others, enzyme replacement therapy is used, where functional ADA enzyme is injected into the patient. However, neither approach gives a complete or permanent cure.
• In gene therapy, lymphocytes are taken from the patient’s blood and grown in culture outside the body.
  A functional ADA cDNA is then introduced into these lymphocytes using a retroviral vector.
  The genetically corrected lymphocytes are then returned to the patient, restoring partial immune function.
• Because these lymphocytes have a limited lifespan, the patient requires periodic infusion of such engineered cells. A permanent cure is possible only if the functional ADA gene is introduced into early embryonic cells or bone marrow stem cells.

Question 6.
Digrammatically represent the experimental steps in cloning and expressing an human gene (say the gene for growth hormone) into a bacterium like E. coli?
Answer: