Cambridge O Level Biology · Syllabus 5090 · Biotechnology and Genetic Modification
Pest resistance
What is Pest resistance?
The increase in frequency of an allele giving resistance, in a pest population exposed to an insect-resistant crop or to an insecticide. Variation already exists in the pest population before the crop is planted, and a few individuals happen to carry an allele that lets them tolerate it. The crop then acts as a selection pressure: susceptible individuals die or reproduce less, while resistant individuals survive, reproduce and pass the allele to their offspring. Over generations the proportion of resistant individuals rises until the crop no longer controls the pest effectively. The crop selects among variation that already existed; it does not cause the mutation, and individual pests do not become resistant during their lifetimes.
This definition is part of the Biotechnology and Genetic Modification chapter in Cambridge O Level Biology.
Pest resistance in context
Biotechnology is the use of living organisms, cells or enzymes to make useful products. Yeast respires anaerobically, converting glucose to ethanol and carbon dioxide: the carbon dioxide raises bread dough, and the ethanol is the product collected in ethanol manufacture. Bacteria are chosen for industrial production because they reproduce rapidly, can make complex molecules, contain plasmids that can receive selected genes, and raise fewer ethical concerns than using animals. They are grown in fermenters, in which temperature, pH, oxygen, nutrient supply and waste products are all controlled. Isolated enzymes do industrial jobs of their own — proteases and lipases in biological washing powders, pectinase in fruit juice, lactase in lactose-free milk. Genetic modification is changing an organism's genetic material by removing, changing or inserting individual genes; inserting the human insulin gene into bacterial DNA lets bacteria make human insulin, and inserting genes into crops can give herbicide resistance, insect-pest resistance or increased vitamin content — each with benefits and risks that have to be weighed rather than declared.
Questions students ask about Pest resistance
What are the three required examples of genetically modified crops?
Herbicide resistance, so the crop survives being sprayed with a particular herbicide and that herbicide can control competing weeds; insect-pest resistance, so the crop is damaged less by particular pests and less insecticide may be needed; and increased vitamin content, where inserted genes raise the production or accumulation of a vitamin or its precursor.