Cloning

Cloning

Genes, cells or whole organisms that carry identical genetic material as they are derived from the same original DNA
Natural - identical twins produced when a zygote splits into two
Asexual - when plants reproduce by producing runners
Bacteria divide asexually by binary fission
Advantages and Disadvantages of asexual reproduction
1. allows organisms to reproduce rapidly and so take advantage of resources in the environment
2. Prokaryotes divide by binary fission, so DNA replicates & cell divides into two. Provided there are no mutations the 2 cells are genetically identical
3. The basis of asexual reproduction in Eukaryotes is mitosis
  1. Genetic material replicates and separates to form two new nuclei, each containing the exact copy of the original DNA
4. it can be completed if sexual reproduction is not possible
5. all offspring have genetic information to enable them to survive in their environment
6. it does not produce any genetic variety, so any genetic parental weakness will be present in the offspring
  1. if environment changes, eg the introduction of a new disease all organisms will be equally susceptible
Natural vegetation propagation in plants
1. The natural production of plant clones from non-reproductive tissues e.g roots, leaves and stems
2. The English elm are adapted to reproduce asexually following damage to the parent plant. Allows species to survive disease or burning.
  1. New growth in the form of root suckers, or basal sprouts appear within 2 months of destruction of the main trunk.
  2. Root suckers help the elm spread as they can grow all around the original trunk
  3. When the tree is stressed or the trunk dies, the suckers grow into a circle of new elms called a clonal patch
  4. However once the new trees get to about 10 cm in diameter, they become infected (by Dutch elm disease)and die
    1. This is as the new trunks are clones of the old one an so they do not have any resistance to the fungal attack
    2. There is also no genetic variation within the cloned population, so natural selection cannot occur
  5. Advantages
    1. One isolated individual can reproduce to eventually colonise a whole area
    2. No reliance on agents of pollination such as wind or insects
    3. Reproduction is faster
    4. No genetic variation so all individuals are equally susceptible to disese
    5. Tubers and bulbs may be edible by humans
    6. Growers can easily propagate many natural clones of individual plants with desirable characteristics
Artificial cloning and agriculture
1. Artificial vegetative propagation
  1. Taking cuttings - section of a stem is cut and treated with plant hormones to encourage root growth and then planted
    1. Genetic uniformity means that all plants are equally susceptible to any new pest, disease or environmental change
  2. Grafting - shoot section of a woody plant is joined to a growing root & stem (rootstock), the graft grows genetically identical to the parent
  3. Farmers know what crop the plant produced will be like as it is cloned from plants with known features
  5. Farmers costs are reduced because all the crop is ready for harvest at the same time
2. Using tissue culture: large-scale cloning
  1. Generates large stocks of a plant quickly and disease free
  2. Micropropagation by callus tissue culture
    1. Small piece of tissue is taken from the plant to be cloned, usually from the shoot tip. Called explant
    2. The explant is placed on a nutrient growth medium
    3. Cells in the tissue divide, forming a mass of undifferentiated cells called a calus
    4. A few week later, single callus cells can be removed from the mass & placed on a growing medium containing plant hormones that encourage shoot growth
    5. Further weeks later, the growing shoots are transferred onto a medium containing different hormone conc that encourages root growth
    6. The growing plants are then transferred to a greenhouse to be acclimatised and grown further before they are planted
Cloning Animals
1. Splitting embryos
  1. Eggs and sperm are collected from two organisms and undergo in vitro fertilisation
  2. Cells from the developing embryo are split into separate segments, to form separate genetically identical organisms
2. Nuclear transfer
  1. A body cell from an adult is taken and its nucleus is placed in an egg cell that has its nucleus removed (enucleated egg cell)
  2. The egg then goes through the stages of development using genetic information from the inserted nucleus
  3. The egg is stimulated to divide and an embryo is formed
    1. In non-reproductive cloning stem cells are harvested from the embryo.
      1. used to make embryonic stem cells that are genetically identical to another organism (therapeutic cloning)
        stem cells have the potential to become any cell type in an organism - to replace damaged tissues in a range of disease e.g heart disease/parkinson's
        If tissue is made from cloned embryonic stem cells that are genetically identical to the patient's own cells then the tissue won't be rejected
        using cloned cells is less dangerous than a major operation such as a heart transplant
        Cloning & cell culture techniques could mean an end to the current problems of waiting for donor organs to become avaliable for transplant
        Cloned cells can be used to generate any cell type as they are totipotent
    2. In reproductive cloning the embryo is implanted into a surrogate mother
      1. Makes a complete organism that is genetically identical to another organism
        cloned animals are used for research purposes - to test new drugs
        used to save endangered animals from extinction by cloning new individuals
        used by farmers to increase number of animals with desired characteristics
3. Advantages and Disadvantage of Cloning Animals
  1. High-value animals, such as cows with high milk yield, can be cloned in large numbers
  2. Rare animals can be cloned to preserve the species
  3. Genetically modified animals such as sheep that produce pharmaceutical chemicals in their milk - can be quickly reproduced
  4. High- value animals are not necessarily produced with animal welfare in mind
  5. Excessive genetic uniformity in a species makes it unlikely to be able to cope with, or adapt to, changes in the environment
  6. Unclear whether animals cloned using the nuclear material of adult cells will remain healthy in the long term
  7. Undesirable genetic characteristics (e.g. a weak immune system) are always passed onto the clones
  8. Ethical Issues
    1. Embryos usually destroyed after the embryonic stem cells have been harvested - destroying human life?

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