Genetic Manipulation
Übersicht
Almost every dessert banana sold on the planet belongs to one variety, and no two of them differ by a single base of DNA. They are not bred from seed. Growers cut shoots from plants that already exist, so the fruit in a market in Lagos and the fruit in a market in London are, genetically, the same plant grown twice. Agriculture has been making copies of living things for centuries, long before anyone knew what a gene was.
This lesson covers the two things biologists can now do deliberately: copy an organism, and rewrite one. You will work through the four cloning techniques the specification names, follow a single gene as it is cut out of one species and delivered into the cells of another, and see why crops built this way raise questions that no experiment on its own can settle. The last part matters as much as the first: OxfordAQA expects you to read unfamiliar information about these techniques and reach a judgement you can defend.
Ziele
- Modern cloning techniques include: tissue culture - using small groups of cells from part of a plant; ‘cuttings’ - an older, but simple, method used by gardeners to produce many identical new plants from a parent plant; embryo transplants - splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers; adult cell cloning - the nucleus is removed from an unfertilised egg cell and the nucleus from an adult body cell, eg a skin cell, is inserted into the egg cell. An electric shock then acts as the catalyst for the egg cell to begin to divide to form embryo cells. These embryo cells contain the same genetic information as the adult skin cell. When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development.
- In genetic engineering, genes from the chromosomes of humans and other organisms can be ‘cut out’ and transferred to cells of other organisms: enzymes are used to isolate the required gene; this gene is inserted into a vector, usually a bacterial plasmid or a virus; the vector is used to insert the gene into the required cells.
- Genes can also be transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics.
- Crops that have had their genes modified in this way are called genetically modified (GM) crops. GM crops include ones that are resistant to insect attack or to herbicides.
- GM crops generally show increased yields.
- Concerns about GM crops include the effect on populations of wild flowers and insects, and uncertainty about the effects of eating GM crops on human health. Students should be able, when provided with appropriate information, to interpret information about cloning techniques and genetic engineering techniques and to make informed judgements about issues concerning cloning and genetic engineering, including GM crops.
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- Which cloning technique uses a small group of cells taken from part of a plant? A. Cuttings B. Tissue culture C. Embryo transplants D. Adult cell cloning Answer: B
- In genetic engineering, what is usually used as a vector? A. A restriction enzyme B. A ribosome C. A bacterial plasmid D. A red blood cell Answer: C
- In adult cell cloning, what is removed from the unfertilised egg cell? A. The cytoplasm B. The cell membrane C. The mitochondria D. The nucleus Answer: D
- In adult cell cloning, what acts as the catalyst that makes the egg cell begin to divide? A. An electric shock B. A rise in temperature C. Adding a plasmid D. Fertilisation by a sperm cell Answer: A
- Which of these is a concern raised about growing GM crops? A. GM crops generally give lower yields B. GM crops cannot be resistant to herbicides C. GM crops may affect populations of wild flowers and insects D. GM crops are clones of each other Answer: C
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