Describe the production of natural clones in plants using the example of vegetative propagation in elm trees
Asexual reproduction in plants occurs through mitosis, as plant cells are eukaryotic, producing genetically identical offspring.
The English elm, Ulmus procera, is adapted to reproduce asexually following damage to the parent plant, allowing the species to survive disasters such as disease or burning. New growth in the form of root suckers, also called basal sprouts, appears within 2 months of the destruction of the main trunk. The suckers grow from meristem tissue in the trunk close to the ground, where least damage is likely to have occurred.
Root suckers help the elm spread as they can grow all around the original trunk. When the tree is stressed or dies, the suckers grow into a circle of new elms called a clonal patch. This in turn sends out new suckers, allowing the patch to expand as far a resources allow.
Describe the production of artificial clones of plants from tissue culture
This is used for large scale cloning as it can generate huge numbers of genetically identical plants from a very small amount of plant material. The most common method used is called micropropagation; many houseplants, like orchids, are produced in this way.
1) A small piece of tissue is taken from the plant to be cloned, usually from the shoot tip. This is called an explant
2) The explant is placed on a nutrient growth medium
3) Cells in the tissue divide, but do not differentiate; instead they formed a mass of undifferentiated cells called a callus
4) After a few weeks, single callus cells can be removed from the mass and placed on a growing medium containing plant hormones that encourage shoot growth
5) After a further few weeks, the growing shoots are transferred onto a different growing medium containing different hormone concentrations that encourage root growth
6) The growing plants are then transferred to a greenhouse to be acclimatised and grown further before they are planted outside
Discuss the advantages and disadvantages of plant cloning in agriculture
- Cloning of artificially/naturally selected high quality crops produced in terms of yield and resistance to environmental conditions such as drought, pests or weeds
- Farmers know what the crop plant produced will be like because it is cloned from plants with known features like taste, colour and disease resistance
- Farmers' costs are reduced because all the crop will be ready to harvest at the same time
- Huge numbers of genetically identical plants can be generated from a single small sample
- Genetically identical crops means that all specimens are equally susceptible to disease, environmental change and pests
- Reduced genetic variation
- Sometimes cloning produces sterile plants which cannot reproduce themselves naturally, so must then always be cloned e.g. bananas
Describe how artificial clones of animals can be produced
There are two ways in which to do this - splitting embryos, or using enucleated eggs.
Cells from a developing embryo can be separated out…