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CLONING CLONING Lecture Notes for Biology

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					CLONING

 Lecture Notes for Biology Today
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.
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.
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
Cloning Vertebrate Animals
   In the 1960’s, 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
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
Cloning Mammals
   In 1997 Ian Wilmut and colleagues in
    Scotland announced the birth of “Dolly” the
    first cloned mammal.
   In a procedure similar to Gurdon’s, 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)
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.
Dolly (cont)
   Dolly developed lung cancer and
    arthritis and was euthanized in 2003 at
    the age of 6 years.
   Most sheep of Dolly’s breed live to 11 or
    12 years.
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.
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/fig_tab/nature723_F1.html
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.
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
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
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
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 woman’s
    uterus to continue development to birth
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
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
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.
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.
Potential Uses of Cloning
Technology
   Gene therapy
   Genetic engineering of organisms
   Sequencing genomes
   Reproductive cloning of animals to
    produce some with special qualities
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
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
Risks of Cloning
   In cloned mice, 4% of the genes
    function abnormally
   Genetic imprinting of sperm-derived vs
    egg-derived genes is not possible
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. 415:859

				
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