Cloning

Cloning

1. Genes, cells or whole organisms that carry identical genetic material as they are derived from the same original DNA

2. Natural - identical twins produced when a zygote splits into two

3. Asexual - when plants reproduce by producing runners

4. Bacteria divide asexually by binary fission

5. Advantages and Disadvantages of asexual reproduction

   • allows organisms to reproduce rapidly and so take advantage of resources in the environment
   • Prokaryotes divide by binary fission, so DNA replicates & cell divides into two. Provided there are no mutations the 2 cells are genetically identical
   • The basis of asexual reproduction in Eukaryotes is mitosis
     • Genetic material replicates and separates to form two new nuclei, each containing the exact copy of the original DNA
   • it can be completed if sexual reproduction is not possible
   • all offspring have genetic information to enable them to survive in their environment
   • it does not produce any genetic variety, so any genetic parental weakness will be present in the offspring
     • if environment changes, eg the introduction of a new disease all organisms will be equally susceptible

6. Natural vegetation propagation in plants

   • The natural production of plant clones from non-reproductive tissues e.g roots, leaves and stems
   • The English elm are adapted to reproduce asexually following damage to the parent plant. Allows species to survive disease or burning.
     • New growth in the form of root suckers, or basal sprouts appear within 2 months of destruction of the main trunk.
     • Root suckers help the elm spread as they can grow all around the original trunk
     • When the tree is stressed or the trunk dies, the suckers grow into a circle of new elms called a clonal patch
     • However once the new trees get to about 10 cm in diameter, they become infected (by Dutch elm disease)and die
       • This is as the new trunks are clones of the old one an so they do not have any resistance to the fungal attack
       • There is also no genetic variation within the cloned population, so natural selection cannot occur
     • Advantages
       • One isolated individual can reproduce to eventually colonise a whole area
       • No reliance on agents of pollination such as wind or insects
       • Reproduction is faster
       • No genetic variation so all individuals are equally susceptible to disese
       • Tubers and bulbs may be edible by humans
       • Growers can easily propagate many natural clones of individual plants with desirable characteristics

7. Artificial cloning and agriculture

   • Artificial vegetative propagation
     • Taking cuttings - section of a stem is cut and treated with plant hormones to encourage root growth and then planted
       • Genetic uniformity means that all plants are equally susceptible to any new pest, disease or environmental change
     • Grafting - shoot section of a woody plant is joined to a growing root & stem (rootstock), the graft grows genetically identical to the parent
     • Farmers know what crop the plant produced will be like as it is cloned from plants with known features
     • Farmers costs are reduced because all the crop is ready for harvest at the same time
   • Using tissue culture: large-scale cloning
     • Generates large stocks of a plant quickly and disease free
     • Micropropagation by callus tissue culture
       • Small piece of tissue is taken from the plant to be cloned, usually from the shoot tip. Called explant
       • The explant is placed on a nutrient growth medium
       • Cells in the tissue divide, forming a mass of undifferentiated cells called a calus
       • 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
       • Further weeks later, the growing shoots are transferred onto a medium containing different hormone conc that encourages root growth
       • The growing plants are then transferred to a greenhouse to be acclimatised and grown further before they are planted

8. Cloning Animals

   • Splitting embryos
     • Eggs and sperm are collected from two organisms and undergo in vitro fertilisation
     • Cells from the developing embryo are split into separate segments, to form separate genetically identical organisms
   • Nuclear transfer
     • 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)
     • The egg then goes through the stages of development using genetic information from the inserted nucleus
     • The egg is stimulated to divide and an embryo is formed
       • In non-reproductive cloning stem cells are harvested from the embryo.
         • 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
       • In reproductive cloning the embryo is implanted into a surrogate mother
         • 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
   • Advantages and Disadvantage of Cloning Animals
     • High-value animals, such as cows with high milk yield, can be cloned in large numbers
     • Rare animals can be cloned to preserve the species
     • Genetically modified animals such as sheep that produce pharmaceutical chemicals in their milk - can be quickly reproduced
     • High- value animals are not necessarily produced with animal welfare in mind
     • Excessive genetic uniformity in a species makes it unlikely to be able to cope with, or adapt to, changes in the environment
     • Unclear whether animals cloned using the nuclear material of adult cells will remain healthy in the long term
     • Undesirable genetic characteristics (e.g. a weak immune system) are always passed onto the clones
     • Ethical Issues
       • Embryos usually destroyed after the embryonic stem cells have been harvested - destroying human life?