Chapter 22

• What kind of cloning is vegetative propagation

  natural cloning
• Vegetative propagation

  • a structure forms which develops into a fully differentiated new plant
  • the new plant may be propagated from the stem, leaf, bud or root of the parent and it eventually becomes independent from its parent
  • often involves perennating organs which enables plants to survive adverse conditions - these contain stored food from photosynthesis & can remain dormant in the soil - often not only a means of asexual reproduction but also a way of surviving from one growing season to the next
• What does natural plant cloning occur in

  • bulbs - e.g. daffodil
  • runners - e.g. strawberry
  • rhizomes - e.g. marram grass
  • stem tubers - e.g. potato
• Using natural clones in horticulture

  • natural cloning is exploited in horticulture by farmers & gardeners to produce new plants
  • splitting up bulbs, removing young plants from runners & cutting up rhizomes all increase plant numbers cheaply & new plants have same genetic characteristics as parents
  • also take cuttings of many plants - short sections of stems are taken & planted directly in ground or in pots - rooting hormone often applied to base of cutting to encourage growth of new roots
• Advantages of propagation from cutting over using seeds

  • faster - time from planting to cropping is much reduced
  • guarantees quality of the plants
  • offspring will be genetically identical & therefore will crop well
• Disadvantages of propagation from cutting

  • lack of genetic variation in offspring if any new disease or pest appear or if climate change occurs
• Cloning sugar cane 


  • one of the fastest growing crop plants in world
• When is micropropagation used to produce plants

  • when a desirable plant doesn't readily respond to seeds
  • doesn't respond well to natural cloning
  • has been genetically modified to or selectively bred with difficulty
  • is required to be pathogen-free by growers - e.g. strawberries, bananas
• Basic principles of micropropagation & tissue culture

  • small, virus-free tissue sample is dissected under sterile conditions to prevent contamination
  • tissue sterilised using agents like bleach
  • explant is place in a sterile culture medium with plant hormones that stimulate cell division forming mass of identical cells (callus)
  • callus cells are transferred to a new medium w diff hormone mix to develop into genetically identical plantlets
  • plantlets potted in compost to grow into small plants & are planted for crop production
• Advantages of micropropagation

  • allows for rapid production of large numbers of plants with known genetic make-up
  • culturing meristem tissue produces disease-free plants
  • makes it possible to produce viable numbers of plants after genetic modification of plant cells
  • provides new way of producing very large numbers of new plants which are seedless & therefore sterile to meet consumer tastes
  • provides way of growing plants which are naturally relatively infertile or difficult to grow from seed
  • provides way of reliably increasing numbers of rare or endangered plants
• Disadvantages of micropropagation

  • produces a monoculture
  • relatively expensive process & requires skilled workers
  • explants & plantlets are vulnerable to infection by moulds & other diseases during the production process
  • if source material is infected w a virus all of there clones will also be infected
  • in some cases large numbers of new plants are lost during process
• What kind of clones are twins?

  natural clones
• Natural cloning in invertebrates

  • can take in several forms
  • some animals (e.g. starfish) can regenerate entire animals from fragments of the original if they are damaged
  • hydra produce small 'buds' on the side of their body which develop into genetically identical clones
  • in some insects offspring produced w/out mating
• Cloning in vertebrates

  • main form = monozygotic (identical) twins
  • early embryo splits to form 2 separate embryos - when born, although genetical identical, they may look diff as result of differences in position & nutrition in uterus
• Natural twinning vs artificial twinning

  • in natural twinning an early embryo splits & 2 foetuses go on to develop from 2 halves of the divided embryo
  • in artificial twinning the split in the early embryo is produced manually - it may be split into more than 2 pieces & results in a number of identical offspring
  • used by farming community to produce max offspring from good dairy or beef cattle or sheep
• Stages of artificial twinning

  • a cow with desirable traits is treated w hormones so she super-ovulates releasing more mature ova than normal
  • ova fertilised naturally or by artificial insemination by a bull w good traits - or mature eggs are removed & fertilised by bull semen in the lab
  • around day 6 when cells of early embryo still totipotent, they are split to produce several smaller embryos
  • each of the split embryo is grown in the lab before implanted into a diff mother (single pregnancies less risky)
  • embryos develop into foetuses & identical cloned animals born by diff mothers
• Why may artificial twinning be useful to a farmer?

  • can clone an animal that produces a high yield
  • maximises yield & profit
• Why can only early embryos be used in artificial twinning?

  • early embryos are totipotent (can become any cell type)
  • once cells start to differentiate they cannot grow into a whole organism
• Why are the embryos grown in the lab after splitting rather than being implanted straight away?

  • to ensure they are developing normally so there is best chance of success
• Why do pigs have multiple embryos implanted into each surrogate mother?

  • pigs normally produce litters so there is more chance of the embryos being rejected
  • implanting multiple embryos increases numbers of offspring produced by the animals with the best genetic stock
• What is somatic cell nuclear transfer (SCNT) used for?

  to clone an adult animal
• Stages of SCNT

  • nucleus removed from somatic cell of adult animal
  • nucleus removed from a mature ovum from a diff female animal of the same species (is enucleated)
  • nucleus from adult somatic animal cell is placed into the enucleated ovum & given a mild electric shock so it fuses & begins to divide
  • embryo that develops is transferred into the uterus of a third animal where it develops to term
  • new animal is a clone of the animal from which the original somatic cell is derived (although mitochondrial DNA will come from egg cell)

  
• What kind of process is SCNT known as

  • reproductive cloning
  • because live animals are end result - the cloned embryo can be split to produce several identical clones
• Problems with SCNT

  • concerns about premature aging (e.g. Dolly the sheep put down at 6 because suffered from arthritis & lung disease)
  • however scientists have improved the technique
• Use of SCNT

  • pharming - production of animals that have been genetically engineered to produce useful products in their milk
  • produce GM animals which grow organs that have potential to be used in human transplants
• Arguments for animal cloning

  • enables high-yielding farm animals to produce more offspring than normal reproduction
  • artificial twinning enables success of passing on desirable to be determined - if first cloned embryo = successful breeding animal, more identical animals can be reared from remaining frozen clones
  • SCNT enables GM embryos to be replicated & develop giving many embryos from one procedure
  • SCNT enables scientists to clone specific animals
  • SCNT has potential to enable rare/ endangered/ extinct animals to be reproduced - nucleus from frozen tissue of dead species transferred
• Arguments against animal cloning

  • SCNT is inefficient - takes many eggs to produce a single cloned offspring
  • many cloned animal embryos fail to develop & miscarry or produce malformed offspring
  • can result in shortened lifespans
  • SCNT relatively unsuccessful so far in increasing populations of rare organisms or allowing extinct species to be brought back to life
• What is biotechnology?

  the industrial use of living organisms (or parts of living organisms) to produce food, drugs or other product
• Why use microorganisms?

  • no welfare issues
  • is an enormous range of microorganisms capable of carrying out diff chemical syntheses or degradations that can be used
  • genetic engineering allows us to artificially manipulate microorganism to carry out synthesis reactions that they would not do naturally
  • microorganisms have short life cycle & rapid growth - can be produced in short periods of time
  • have simple and cheap nutrient requirements
  • simple conditions - make bioprocesses relatively chwap
• Advantages of using microorganisms to produce human food

  • reproduce fast & produce protein faster than animals & plants
  • have high protein content with little fat
  • can use a wide variety of waste materials including human & animal waste, reducing costs
  • can be genetically modified to produce protein required
  • production not dependent on weather, breeding cycles etc - takes place constantly & can be increased/ decreased to match demand
  • no welfare issues
  • can be made to taste like anything
• Disadvantages of using microorganisms to produce human food

  • some can produce toxins if conditions not maintained at optimum
  • have to be separated from nutrient broth & processed to make food
  • need sterile conditions that are carefully controlled - adds to costs
  • often involve GM organisms & many people have concerns about eating GM food
  • protein has to be purified to ensure it contains no toxins or contaminants
  • many dislike thought of eating microorganisms grown on water
  • has little natural flavour - needs additives
• What is culturing?

  growing large enough numbers of microorganisms for us to see them clearly with the naked eye
• Why do health & safety procedures need to be followed when microorganisms are cultured?

  • there is always risk of mutation taking placing making the strain pathogenic
  • there may be contamination with pathogenic microorganisms from the environment
• Conditions when culturing microorganisms

  • need right conditions of temp, oxygen & pH
  • nutrient medium = food provided for microorganisms
  • nutrients added to agar or broth to provide a better medium for microbial growth
  • nutrient medium must be kept sterile until ready for use - aseptic techniques important
• When culturing microorganisms when is bacteria added?

  once agar or nutrient broth is prepared the bacteria must be added in process called inoculation
• Inoculating broth

  • make a suspension of the bacteria to be grown
  • mix a known volume with the sterile nutrient broth in the flask
  • stopper the flask with cotton wool to prevent contamination from air
  • incubate at suitable temp, shaking regularly to aerate the broth providing oxygen for growing bacteria
• Inoculating agar

  • wire inoculating loop sterilised by holding in a Bunsen flame until it glows red hot - must not touch any surfaces as it cools
  • dip sterilised loop in bacterial suspension - remove lid of Petri dish & make zig-zag streak across surface of agar
  • replace lid of Petri dish - should be held down with tape but not sealed completely so oxygen can get in, preventing growth of anaerobic bacteria
  • incubate at suitable temp
• Why is inoculation loop heated until it is red hot?

  to remove/ kill any contaminating microorganisms
• Why is the inoculation loop cooled before it is used to collect a sample of microorganisms?

  to avoid killing the desired microorganisms
• Why is all work carried out next to a lit bunsen?

  updraft helps minimise contamination