GM Crops - Fewer Chemicals, Smaller Losses
Genetic modification changed farming in several practical ways. Transgenic crops that carry their own defence against insects have reduced reliance on chemical pesticides, so the farmer sprays less. GM crops have also helped to reduce post-harvest losses - the produce spoilt after the crop is gathered from the field. GM plants are also more tolerant to abiotic stresses, use minerals more efficiently, and have enhanced nutritional value.
The Bt crystal
Some strains of Bacillus thuringiensis form protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein - that is what makes the bacterium useful, and cloning this gene into plants created a bio-pesticide. The bacterium is unharmed because the protein is stored as an inactive protoxin, which turns toxic only in the alkaline gut of an insect that eats it.
Protecting a plant from a nematode
The nematode Meloidogyne incognita infects tobacco roots and greatly reduces yield. To stop it, nematode-specific genes were introduced into the host plant using Agrobacterium vectors. The DNA was introduced in such a way that the host cells produced both sense RNA and antisense RNA. Being complementary, these two strands paired to form double-stranded RNA (dsRNA), which set off RNA interference (RNAi) and silenced the nematode's specific mRNA. The parasite could not survive in such a host, so the transgenic plant protected itself.
One-liners: GM crops -> less chemical pesticide, less post-harvest loss; B. thuringiensis crystal = toxic insecticidal protein; nematode resistance -> Agrobacterium vectors, host makes sense + antisense RNA -> dsRNA -> RNAi.
Recombinant Therapeutics and Gene Therapy
Before recombinant technology, insulin for diabetics was extracted from the pancreas of slaughtered cattle and pigs. To the human body this is a foreign protein, so animal-source insulin caused some patients to develop allergy or other types of immune responses. Human insulin made in bacteria removed that difficulty, since a drug produced in a human form does not provoke unwanted immunological responses. About 30 recombinant therapeutics have been approved for human use the world over, and 12 of these are presently being marketed in India.
Gene therapy corrects a defect by delivering a functional gene. The standard example is adenosine deaminase (ADA) deficiency, caused by deletion of the gene for this enzyme, which the immune system needs. Besides gene therapy, two treatments are used: bone-marrow transplantation cures some children, and enzyme replacement therapy, in which functional ADA is given to the patient by injection, helps others. Neither is completely curative, which is why gene therapy was attempted.
One-liners: animal insulin -> allergy / immune response to a foreign protein; 30 recombinant therapeutics approved worldwide, 12 marketed in India; ADA treatments other than gene therapy = bone-marrow transplantation and ADA by injection.
Diagnosis, Animal Models and Biopiracy
Molecular methods detect disease long before symptoms appear. In probe-based diagnosis, a single-stranded DNA or RNA tagged with a radioactive molecule - the probe - is hybridised with the patient's DNA and read by autoradiography. A clone carrying a mutated gene does not appear on the photographic film, because the probe cannot pair with the altered sequence. ELISA rests on antigen-antibody interaction: infection is detected either by the antigens of the pathogen or by the antibodies synthesised against the pathogen.
Transgenic animals also serve as models of human disease, so that new treatments can be investigated. Models exist for cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's disease, and similar attempts are being made for phenylketonuria (PKU) and cystic fibrosis.
Indian bio-resources and traditional knowledge - Basmati rice being the best-known case - were patented abroad without proper authorisation and without compensatory payment. This injustice pushed nations to frame laws against unauthorised exploitation of their bio-resources, and the Indian Parliament cleared the second amendment of the Indian Patents Bill to address such issues.
One-liners: probe = single-stranded DNA/RNA + radioactive tag; ELISA detects pathogen antigens or antibodies against it; models = cancer, cystic fibrosis, rheumatoid arthritis, Alzheimer's; biopiracy -> laws + second amendment of Indian Patents Bill.