CLONING

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CLONING

• Lecture Notes for Biology Today

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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.

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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.

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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

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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

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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

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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)

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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.

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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.

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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.

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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

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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.

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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

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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

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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

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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

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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

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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

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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.

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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.

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Potential Uses of Cloning Technology

• Gene therapy
• Genetic engineering of organisms
• Sequencing genomes
• Reproductive cloning of animals to produce some
  with special qualities

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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

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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

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Risks of Cloning

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

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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