The mammal copiers – advances in cloning
Box 1 | Propagating plants
Gardeners propagate some of their favourite plants by inducing root growth in cuttings. Some hasten the process by dipping the bottom end of each cutting into an auxin, a plant growth regulator that promotes root growth.
Horticulturalists use a technique called tissue culturing to propagate plants. They cut off a small piece of tissue (called an explant), wash it in sodium hypochlorite bleach to kill any micro-organisms on the surface, and place it on nutrient agar in a culture tube to grow. Sterile conditions are maintained throughout the procedure otherwise the explant would be swamped by micro-organisms growing on the nutrient medium.
The explant, usually a bud, is cultured first on a medium containing a fairly high concentration of a cytokinin. Cytokinins are substances that stimulate cell division, and the one used in this procedure induces the outgrowth of shoots. When the explant has produced many shoots it is dissected into more explants, each of which is placed in a new tube of culture medium. This subculturing can be carried on indefinitely to produce large numbers of clones. To obtain plants, the subcultured shoots are transferred to a culture medium containing a moderately high concentration of an auxin to promote root growth. After the roots develop, the plants are transferred to soil to grow.
Species propagated commercially by tissue culture in Australia include Australian natives, indoor foliage plants, crop plants and ornamentals. A commercial laboratory starts with hundreds of explants and produces thousands of new plants in a year.
Boxes
Box 2. How Dolly the sheep was cloned
Box 3. On human cloning: A position statement from the Australian Academy of Science
Posted May 1999.