Biotechnology

🌾Selective breeding

In selective breeding (artificial selection), humans choose individuals with desired characteristics and breed them together, then choose the best offspring and repeat over many generations. Examples: high-yielding rice varieties such as those of the Green Revolution, cattle that produce more milk, disease-resistant crops, and every breed of dog. It is slow and imprecise, and it reduces genetic variation: inbreeding can bring out harmful recessive alleles, and a uniform crop can be wiped out by one new disease.

🧬Genetic modification

Genetic modification (genetic engineering) transfers a gene from one organism into another, even of a different species, giving it a new characteristic. The result is a genetically modified organism (GMO).

1. The gene is cut out of the donor DNA using restriction enzymes, which cut at specific base sequences.
2. A vector, usually a bacterial plasmid, is cut with the same enzyme.
3. The gene is joined into the plasmid by the enzyme ligase.
4. The plasmid is taken up by the host cell (a bacterium, or a plant or animal cell).
5. Host cells that took up the gene are selected and grown, and the gene is expressed — the new protein is made.

Examples: bacteria that make human insulin for people with diabetes (replacing insulin extracted from pigs and cattle); Bt crops with a bacterial gene that makes an insecticidal protein, reducing spraying; herbicide-resistant crops; Golden Rice, engineered to make beta-carotene, which the body turns into vitamin A, to reduce childhood blindness where rice is the staple food.

👧Cloning

• Cuttings — a piece of stem is planted and grows roots (helped by rooting powder containing auxin).
• Tissue culture (micropropagation) — small groups of cells are grown on sterile nutrient jelly with hormones, producing thousands of identical plants, used for orchids and bananas.
• Embryo transplants — an early embryo from high-quality animals is split and the parts are implanted in surrogate mothers.
• Adult cell cloning — the nucleus of a body cell is put into an egg cell whose nucleus has been removed; an electric shock starts division, and the embryo is implanted. Dolly the sheep (1996) was the first mammal cloned this way.

🧫Microorganisms, stem cells and gene editing

Microorganisms have long been used in biotechnology: yeast in bread and alcohol, bacteria in yoghurt, and the fungus Rhizopus that binds soybeans into tempeh. Industrial fermenters grow microorganisms at controlled temperature, pH and oxygen to make antibiotics (penicillin from a mould), enzymes and mycoprotein.

Stem cells (Topic 2) might be used to grow replacement tissue. Gene editing with CRISPR-Cas9 lets scientists change a specific base sequence precisely; it has been used to treat sickle-cell disease, but editing human embryos, whose changes would be inherited, is banned in most countries.