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CLONING

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CLONING Lecture Notes for Biotechnology What is Cloning? To most people, the term cloning means making a copy of an individual. In biology, cloning can have ... – PowerPoint PPT presentation

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Title: CLONING


1
CLONING
  • Lecture Notes for Biotechnology

2
What is Cloning?
  • To most people, the term cloning means making a
    copy of an individual.
  • In biology, cloning can have different uses
    depending on what is being copied.

3
Cloning Molecules and Cells
  • DNA makes a copy when it replicates to make two
    molecules
  • A cell divides by mitosis to make two identical
    daughter cells.

4
Cloning Organisms
  • Botanists and home gardeners have been cloning
    plants for centuries take a cutting or piece
    of a plant and put in soil and it will form a new
    plant.
  • Animals that reproduce by asexual reproduction,
    such as small female freshwater crustaceans,
    produce offspring which are genetic copies of the
    mother

5
Cloning Vertebrate Animals
  • In the 1960s, John Gurdon experimented with a
    technique called nuclear transplantation
  • He destroyed the nuclei of unfertilized eggs of
    the African clawed toad with UV light and
    replaced them with nuclei taken from intestinal
    cells of tadpoles of the same species

6
Gurdon (cont)
  • A small percentage of the eggs with the
    transplanted nuclei developed past the cleavage
    stage into tadpoles and adults
  • Later experiments using the transplanted nuclei
    from adult toad skin, kidney, heart and lung
    cells produced the same results

7
Cloning Mammals
  • In 1997 Ian Wilmut and colleagues in Scotland
    announced the birth of Dolly the first cloned
    mammal.
  • In a procedure similar to Gurdons, called
    somatic cell nuclear transfer, the lab group
    removed the nuclei from cells in the mammary
    gland of a sheep and placed them in enucleated
    eggs of another sheep.
  • This link shows images of somatic cell nuclear
    transfer (http//www.advancedcell.com/scnt.htm)

8
Dolly (cont)
  • The eggs were stimulated to begin dividing by
    treating them with either chemicals or
    electricity
  • Some of the eggs starting cleaving and were
    placed in the uteruses of other sheep. Only one
    attempt of 277 was successful, producing Dolly.

9
Dolly (cont)
  • Dolly developed lung cancer and arthritis and was
    euthanized in 2003 at the age of 6 years.
  • Most sheep of Dollys breed live to 11 or 12
    years.

10
Other Cloned Mammals
  • Since Dolly, other mammal species have been
    successfully cloned.
  • These include cow, goat, cat, pig, mule and gaur.
  • In many of these attempts, such as the one
    producing CC the kitten, the donor nucleus is not
    removed from its cell but the donor cell is fused
    with an enucleated egg.

11
CC the Kitten
  • Click on the link below to see Copy Cat (CC) the
    cloned kitten (Nature, 2002)
  • CC has a different coat coloration, so she is not
    identical to the nucleus donor
  • http//www.nature.com/nature/journal/v415/n6874/fi
    g_tab/nature723_F1.html

12
CC the Kitten
  • CC is result of the fusion of a donor cumulus
    cell and a recipient egg
  • She is the sole live birth of 188 nuclear
    transfer procedures. 82 produced blastocysts.

13
Cloning Human Cells
  • Researchers distinguish between therapeutic and
    reproductive cloning
  • In therapeutic cloning, the cloned egg is allowed
    to divide for a few days and then the cells are
    separated from each other and saved as stem cells
    for potential use to treat diseases

14
Cloning Human Cells
  • In 2001 a Worcester, MA company called, ACT,
    announced the first human cloning. Of eight
    cloned eggs, only one made it to the six-cell
    stage
  • Later, a ban was put on this type of research by
    the US government if it was supported by public
    funds

15
Cloning Human Cells
  • Research continues in other countries and
    privately-funded labs in the US
  • Recently scientists in South Korea announced they
    successfully cloned a human embryo to the
    blastocyst stage and then separated the cells to
    begin stem cell lines

16
Cloning Human Cells
  • In reproductive cloning, the cloned egg would be
    allowed to divide the the blastocyst stage and
    the the embryo would be implanted into a womans
    uterus to continue development to birth

17
Cloning Human Cells
  • A few years ago, a group called the Raelians,
    announced the birth of a cloned human baby
  • They offered no scientific evidence to support
    their claim and it was dismissed by the
    scientific community

18
Are Clones Identical Copies?
  • As shown by CC the kitten, clones may not be
    identical to the nuclear donor
  • The uterine environment has an influence on
    development
  • Another reason may be the source of the
    mitochondria for the cloned embryo

19
Are Clones Identical Copies?
  • Mitochondria have their own circular strand of
    DNA coding for genes involved with their
    structure and function.
  • Mitochondrial genetic mutations cause several
    genetic diseases
  • Mitochondria are usually only maternally derived,
    the sperm does not supply any to a zygote.

20
Are Clones Identical Copies?
  • In strict nuclear transfer, the mitochondria
    would be supplied by the recipient cell not the
    nuclear DNA donor.
  • In the cell fusion technique, the mitochondria
    would come from both cells.

21
Potential Uses of Cloning Technology
  • Gene therapy
  • Genetic engineering of organisms
  • Sequencing genomes
  • Reproductive cloning of animals to produce some
    with special qualities

22
Other Potential Uses
  • Reproductive cloning of animals to repopulate
    endangered species. This has already been done
    with the gaur, a wild ox, and a mouflon, a wild
    sheep.
  • Therapeutic cloning to produce whole organs for
    transplants in humans
  • Therapeutic cloning to produce healthy cells to
    replace diseased cells

23
Risks of Cloning
  • The technique rarely works and is very expensive
  • Cloned animals, like Dolly, do not live long and
    have a variety of aliments
  • A third of cloned calves born alive die young and
    many are abnormally large

24
Risks of Cloning
  • In cloned mice, 4 of the genes function
    abnormally
  • Genetic imprinting of sperm-derived vs
    egg-derived genes is not possible

25
References
  • http//www.ornl.gov/sci/techresources/Human_Genome
    /elsi/cloning.shtml
  • Prentice, D. A. 2003. Stem Cells and Cloning.
    Benjamin Cummings
  • Cell biology A cat cloned by nuclear
    transplantation. 2002. Nature. 415859
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