GENETIC ENGINEERING OF COTTON FOR INSECT RESISTANCE The DNA code mostly contains instructions for protein synthesis. The code is read in groups of three nucleotides and each triplet of nucleotides codes for one of the twenty amino acids which link together in a polypeptide chain to form a protein. The code is universal, so the same code applies in nearly all living organisms. Some triplets have special functions and direct protein synthesis to start or stop. Protein synthesis occurs in ribosomes where a copy of the gene coding for a protein (mRNA) is translated to produce a protein. Some proteins may be consist of several polypeptide chains and the genes required to do this are collectively called a transcription unit. Fig. 2 Diagram showing how genes code for proteins Bacterium also contain small circular loops of DNA called plasmids which are not essential to the bacterium but can be useful in certain environmental conditions such as resistance to antibiotics. Because bacterium are prokaryotic and don’t have a nucleus plasmids are easy to obtain in pure form and can be introduced into other cells. Plasmids are also capable of independent self-replication, which makes them useful in multiplying useful DNA. Bacteria also produce
eads to it having an altered phenotype. The plant can then produce the Bt Toxin in its leaves through protein synthesis. This then crystallises and when an insect eats the protein it reacts in the insect’s gut and kills the insect within 24 hours. This altered genotype and phenotype will increase the chances of survival of the cotton plants against the cotton budworm (Helicoverpa) and the native budworm (H. puntigera). The protein produced by the plant is only toxic to these pests and will only be activated in the gut of these pests. The gene shouldn’t transfer into other plants that are related to cotton or disturb natural ecological systems. It is possible, however, that the gene may enter a wild strain of cotton may and this would increase the survival chances of the cotton in the wild. The genetic application will ultimately decrease the survival chances of the two types of budworm, but if they are continuously exposed to the toxin they may eventually develop resistance to the toxin. A mutation causing resistance to the toxin could occur in the budworm enabling it to survive the toxin. This mutant strain would breed successfully because it would have no other competition and can pass the gene to future generations. The Bt cotton would therefore have an indirect impact on the genotype of the cotton budworm through the mechanism of natural selection. Issue related to genetically engineering cotton for insect resistance The subject of developing new varieties of plants raises the issue of whether companies should be able to patent the techniques used to make transgenic plants for future profits. In 1991 and 1992 the USA based biotechnology compa
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