A2/A-level Biology - Biotechnology and Gene Technologies (2)

• 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.

1.    A small piece of tissue is taken from the plant to be cloned, usually from the shoot tip (meristem) – explant.
2.    The explant is placed on a nutrient growth medium.
3.    Cells in the tissue divide. They do not differentiate, but form a mass of undifferentiated cells – 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 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.

• Micropropagation is much faster than selective breeding – huge numbers of genetically identical plants can be generated from a single plant.
• Farmers know what the crop plant produced will be like – cloned from plants with known features.
• Farmers’ costs are reduced because all crops are ready for harvest at the same time.
• Allows new plants to be grown, which usually can only be grown from seed, e.g. fruit trees, as the tree from seed would have a combination of genes that would not give the correct tree.
• Some plants are sterile so have to be grown by cloning, e.g. bananas.
• Asexual reproduction is faster than sexual reproduction.
• Asexual reproduction can be a ‘back up’ plan to sexual production if there is a lack of wind or pollinators.   

• All the plants will be susceptible to any new pest, disease or environmental change, e.g. the potato famine in Ireland between 1845 and 1851.
• No genetic diversity/variation – unable to adapt to changing conditions so they’re all likely to die if conditions change.

Do you know how artificial clones of animals can be produced in A2/A-level Biology?

• These cells are totipotent stem cells and they are 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.

• 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.

1.  Collect eggs from a high-value female (e.g. high milk yield in cows) and collect sperm from a high-value male.
2. In vitro fertilisation occurs between the eggs and the sperm.
3. Grow the in vitro to a 16-cell embryo.
4. Split the embryo into several separate segments and implant into surrogate mothers.
5. 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.

1. Remove:
   - mammary cells from Finn Dorset and place in culture.
   - an ovum (egg) from Scottish Blackface
   - the nucleus to produce an enucleate ovum.
2. Electro-fuse the mammary cell and enucleate ovum together to create a reconstructed cell with Scottish Blackface cytoplasm and Finn Dorset nucleus.
3. ‘Culture’ in tied oviduct in sheep.
4. Recover the early embryo and implant the embryo in surrogate mother ewe’s uterus.
5. ‘Dolly’, a Finn Dorset Ewe is born.

• High-value animals, for example cows giving high milk yield, can be cloned in large numbers.
• Rare animals can be cloned to preserve the species.
• Genetically modified animals, for example sheep that produce pharmaceutical chemicals in their milk, can be quickly reproduced.
• Splitting embryo maintains variation whilst giving desired traits.

• High-value animals are not necessarily produced with animal welfare in mind.
  - Some strains of meat-producing chicken have been developed that are unable to walk.
• Excessive genetic uniformity in a species makes it unlikely to be able to cope with, or adapt to, changes in the environment.
• It is still unclear whether animals cloned using the nuclear material of adult cells will remain healthy in the long-term.
  - Dolly the sheep was put down at the age of 6, suffering from a form of lung cancer caused by a virus.
• Splitting embryos does not guarantee results.
• There is a lot of life lost during the cloning process.

That's the end of the topic!

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