Cloning in Plants and Animals
- outline the differences between reproductive and non-reproductive cloning
Clones – genes, cells or whole organisms that carry identical genetic material because they are derived from the same original DNA.
Reproductive cloning generates genetically identical organisms.
Non-reproductive cloning generates cells, tissues and organs – can replace those damaged by diseases or accidents.
The advantages of using cloned cells include:
- Cells won’t be rejected as they’re genetically identical to an individual’s own cells.
- Prevent waiting for donor organs to become available for transplant.
- Cloned cells can be used to generate any cell type because they are totipotent. Damage caused by some diseases and accidents cannot currently be repaired by transplantation or other treatments.
- Using cloned cells is less likely to be dangerous than a major operation such as a heart transplant.
There are many possibilities for non-reproductive cloning, including:
- The regeneration of heart muscle cells following a heart attack.
- The repair of the nervous tissue destroyed by diseases such as multiple sclerosis.
- Repairing the spinal cord of those paralysed by an accident that results in a broken back or neck.
These techniques are often referred to as therapeutic cloning. However, there are some ethical issues concerning whether cloning should be used in humans. There are ethical objections to the use of human embryonic material and some scientific concerns about a lack of understanding of how cloned cells will behave over time.
- describe the production of natural clones and in plants using the example of vegetative propagation in elm trees
Natural Vegetative Propagation:
Vegetative propagation is form of asexual reproduction of a plant. Only one plant is involved and the offspring is the result of one parent. The new plant is genetically identical to the parent.
- Runners – stems that grow horizontally above the ground. They have nodes where buds are formed, which grow into a new plant, e.g. strawberries and spider plant.
- Tubers – new plants will grow out of swollen modified roots called tubers. Buds develop at the base of the stem and then grow into new plants, e.g. potato and daliahs.
- Bulbs – a bulb contains an underground stem, with leaves containing stored food At the centre of the bulb is an apical bud, which produces leaves and flowers. Also attached are lateral buds, which produces new shoots, e.g. daffodils.
- Basal sprouts (root suckers) – the suckers grow from meristem tissue in the trunk close to the ground, where least damage is likely to have occurred, e.g. elm trees and mint. Root suckers help the elm spread, because they can grow all around the original trunk. When the trunk dies, the suckers grow into a circle of new elms called a clonal patch. This, in turn, puts out new suckers so that the patch keeps expanding as far as resources permit.
- describe the production of artificial clones of plants from tissue culture
Artificial Vegetative Propagation:
- Taking Cuttings – e.g. geraniums, a section of the stem is cut between leaf joints (nodes). The cut end of the stem is then often treated with plant hormones to encourage root growth, and planted. The cutting forms a new plant, which is a clone of the original parent plant.
- Grafting – e.g. fruit tree or rosebush, a rootstock is cut to match the wedge-shaped stem to be grafted. The vascular tissue is lined up then binding is wrapped around the graft area to hold it in place until growth supports the grafted section. The graft grows and is genetically identical to the parent plant, but the rootstock is genetically different.
- Using Tissue Culture – used in order to generate huge numbers of genetically identical plants successfully from a very small amount of plant material. The most common method used in the large-scale cloning of plants is micropropagation, e.g. orchids.
- A small piece of tissue is taken from the plant to be cloned, usually from the shoot tip (meristem) – explant.
- The explant is placed on a nutrient growth medium.
- Cells in the tissue divide. They do not differentiate, but form a mass of undifferentiated cells – callus.
- 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.
- After a few weeks, the growing shoots are transferred onto a different growing medium containing different hormone concentrations that encourage root growth.
- The growing plants are then transferred to a greenhouse to be acclimatised and grown further before they are planted outside.
- describe how artificial clones of animals can be produced
Totipotent – stem cells capable of differentiating into any type of adult cell found in the organism.
In animals, only embryonic cells are naturally capable of going through the stages of development in order to generate a new individual. These cells are totipotent stem cells and they are capable of differentiating into any type of adult cell found in the organism. There are two methods of artificially cloning animals:
Method 1: Splitting Embryos
Cells from a developing embryo can be separated out, with each one then going on to produce a separate, genetically identical organism.
- Collect eggs from a high-value female (e.g. high milk yield in cows) and collect sperm from a high-value male.
- In vitro fertilisation occurs between the eggs and the sperm.
- Grow the in vitro to a 16-cell embryo.
- Split the embryo into several separate segments and implant into surrogate mothers.
- Each calf produced is a clone.
Method 2: Nuclear Transfer
A differentiated cell from an adult can be taken, and its nucleus placed in an egg cell which has had its own nucleus removed (enucleated cell). The egg then goes through the stages of development using genetic information from the inserted nucleus. The first animal cloned by this method was Dolly the sheep in 1996, which was successful after 277 attempts.
- Remove mammary cells from Finn Dorset and place in culture. Remove an ovum (egg) from Scottish Blackface and remove the nucleus to produce an enucleate ovum.
- Electro-fuse the mammary cell and enucleate ovum together to create a reconstructed cell with Scottish Blackface cytoplasm and Finn Dorset nucleus.
- ‘Culture’ in tied oviduct in sheep.
- Recover the early embryo and implant the embryo in surrogate mother ewe’s uterus.
- ‘Dolly’, a Finn Dorset Ewe is born.