question_answer

Transgenic crops or genetically modified crops are being cultivated in many parts of the world. One of the main objectives of their production is to minimise the use of insecticides on cultivated crops. Explain with the help of a suitable example, how these genetically modified crops have been developed.

Or

Expand the name of the enzyme ADA. Why is the enzyme essential in the human body? Suggest a gene therapy for its deficiency.

Answer:

One of the objectives of preparing transgenic crops is to make them resistant against pests. It can be explained by taking the example of Bt-cotton. The pest that destroys the cotton balls are cotton bollworms and cotton borer. Bt cotton is created by using some strains of a bacterium, Bacillus thuringiensis (Bt).

This bacterium produces protein that kills certain insects such as lepidopterans (tobacco budworm and armyworm), coleopterans (beetles) and dipterans (flies and mosquitoes). Bacillus thuringiensis forms protein crystals during a particular phase of growth. These crystals contain a toxic insecticidal protein. Bt toxin protein exists as an inactive protoxin, but once an insect ingests the inactive toxin, it gets converted into an active form due to the alkaline pH of the gut which solubilises the crystals. The activated toxin binds to the surface of midgut epithelial cells and creates pores that causes cell swelling and lysis, leading to the death of insect. Genetically modified Bt crops are prepared by introducing Br - genes in the corps.

It involves following steps.

(i) Specific Br toxin genes were isolated from Bacillus thuringiensis - and incorporated into several crop plants.

(ii) Most Bt toxins are insect - group specific. Hence, the toxin is coded by a gene named cry. e.g., the proteins encoded by the genes cry IAc and cry IAb control the cotton bollworms and cry IAb controls corn borer.

Or

The expanded form of ADA is Adenosine Deaminase. It is required for the proper functioning of the immune system. Gene therapy for ADA deficiency

It involves following steps

(i) Lymphocytes from the blood of patient are grown in culture media outside the body.

(ii) A functional ADA, i.e. cDNA (using a retroviral vector) is introduced into these lymphocytes.

(iii) Genetically engineered lymphocytes are returned to the blood of the patient.

(iv) These cells are not immortal, therefore the periodic infusion of such genetically engineered lymphocytes is required by the patient.

(v) If the gene isolated from bone marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.