Cloning

• Natural clones are produced by asexual reporduction
• The advantages of natural cloning are:

  1. If the conditions of growth are good for the parent, they will be good for the offspring
  2. Cloning is relatively rapid, population can increase quickly to take advantage of the optimal conditions
  3. reproduction can still be carried out even if there's only one parent
• The disadvantages for natural cloning are:

  1. offspring may become overcrowded
  2. No genetic diversity (except any caused by mutations)
  3. population will show little variation
  4. selection is not possible
  5. If the environment changes to be less advantageous, the whole environment will be susceptible
• Plants clone via vegetative propagation as some parts of the plant are able to divide and differentiate into a range of cell types. Occurs through vegetative (usually over-wintering organ) parts of the plant as opposed to specialised reproductive structures.
• The different types of methods for vegetative propagation are:

  1. runners
  2. stolons
  3. rhizomes
  4. suckers
  5. bulbs
  6. corms
  7. leaves
• Runners/stolons - stems that grow horizontally along the ground from the base of the plant, producing roots at intervals which eventually develop into new plants. E.g strawberries
• Rhizomes - modified underground stem that grows horizontally just below the surface of the soil. Produces lateral branches with leaves and flowers above the ground. New plants grow from these. E.g ginger
• suckers- shoots that grow from the base of the stem and form new plants. horizontal branch may die and leave the new stem as a separate individual e.g. lilac and cherries
• bulbs-over-wintering mechanism for many perennial monocotyledonous plants. Consist of underground stem which grow a series of fleshy leaf bases. Apical bud will grow into new plant e.g. onion and hyacinth
• corms- similar to bulbs but are solid rather than fleshy. underground stem with scaly leaves and buds e.g. taro
• leaves- clones grow on leaf margins as it reproduces asexually. immature plants drop off and take root e.g. kalanchoe
• tubers- underground stem, on original tuber will grow into more plants. each new plant can later produce more tubers e.g. potatoes
• The different types of plant cutting are:

  • root cutting- buried just below soil surface and produces new shoots
  • scion cutting- dormant woody twigs
  • leaf cuttings- placed in moist soil. develops stems and roots, may produce new plant from one cutting.
• an example of tissue culture is micropropagation
• Steps for micropropagation

  1. Suitable tissue is selected and cutting is made (explant), usually meristematic tissue as its free from viruses

  2. Explant is sterilised using dilute bleach or alcohol (kill any microbes which would thrive in these conditions but not killing sample)

  3. Explants placed on sterile growth medium e.g. agar gel containing suitable nutrients (amino acids, glucose, phosphates)

  4. High concentration of auxins and cytokinins stimulates explant cell division by mitosis to form callus (totipotent cells)

  5. Callus divides to form a larger number of small clumps of undifferentiated cells

  6. Clumps stimulated to grow, divide and differentiate. Achieved by moving cells into different growth medium. 100 auxin:1 cytokinin (root formation) 4 auxin:1 cytokinin (shoot formation)

  7. After platelets have formed, they are transferred to a greenhouse to be grown in compost of soil and acclimatise to normal growing conditions
• What are the two types of artificial cloning?

  embryo twinning/splitting

  SCNT (Somatic Cell Nuclear Transfer)
• describe embryo splitting

  1. eggs are collected from mother and sperm collected from father
  2. in vitro fertilisation takes place
  3. embryo grows in vitro until it has divided into 16 cells (any more divisions and the cells are no longer totipotent)
  4. embryo is split into 4 segments which are then implanted into surrogate mothers
  5. 4 genetically identical offspring are produced
• disadvantages of embryo splitting

  there's no guarantee that the desirable trait has been passed onto offspring. you have to wait for animal to mature to see if the phenotype is presented.
• describe SCNT

  1. Remove mammary cells from udder of animal you wish to clone
  2. culture mammary cells
  3. remove ovum from surrogate mother
  4. remove nucleus from ovum
  5. use electro-fusion so the nucleus of the mammary cell can be inserted into the enucleated cell
  6. culture in tied oviduct of surrogate mother
  7. recover early embryo
  8. implant embryo into surrogate's uterus
  9. clone baby born
• disadvantage of SCNT

  offspring may not be 100% identical as it has mitochondrial DNA of ovum donor
• what is an example of non-reproductive cloning?

  therapeutic cloning
• what are some applications of therapeutic cloning?

  • skin can grow in vitro and act as a graft over burn patients
  • cloned cells have been used to repair damage to the spinal cord of a mouse and restore capability to produce insulin in pancreas
  • potential to grow whole new organs to replace diseased organs

  cells will be genetically identical to recipient so there's no risk of rejection
• arguments for artificial cloning in animals

  1. Can produce whole herd of animals with a high yield or showing unusual characteristics e.g. producing silk in milk
  2. produces genetically identical copies of high value individuals
  3. good for research as there's no interference from different genotypes (investigating genes and hormones)
  4. Can be used for pharmaceutical testing rather than people and animals
  5. can produce tissues genetically identical to donor so can repair damage caused by disease or accidents
  6. endangered species can be cloned
• arguments against artificial cloning in animals

  1. lack of genetic variation, so susceptible to pests and disease
  2. little regard for animal welfare e.g. meat-producing chickens cannot walk
  3. success rate of adult cell cloning is low and cost is high. Clones animals may be less healthy and have shorter life spans
  4. ethical issues regarding how long embryo survives and whether it is right to create a life to destroy it