Cloning involves making genetically identical copies of organisms through somatic cell nuclear transfer. John Gurdon first cloned frogs in the 1960s by transferring nuclei from intestinal cells into enucleated eggs. His work established the basis for cloning techniques still used today. Therapeutic cloning uses somatic cell nuclear transfer to generate patient-matched stem cells for research and potential medical treatments without creating human clones. However, technical challenges remain such as immune rejection and ethical issues around embryo use and destruction.
2. Cloning
It is a process for making numerous copies of
organisms or cells or of individual genes which
are genetically identical.
It refers to the transfer of somatic cell’s nucleus
into an ovum, which then grows into an embryo
3. History
1952
Thomas J. King and Robert Briggs
Northern leopard frogs
1962:
John Gurdon
South African frogs
4. Early Frog Experiments
(gurdon’s Method)
John Gurdon began cloning experiments using non-
embryonic cells
Cells from intestinal lining of tadpoles
Exposed a frog egg to ultraviolet light, which
destroyed its nucleus
Removed the nucleus from the tadpole intestinal
cell and implanted it in the enucleated egg
Egg grew into a tadpole that was genetically identical
to the DNA-donating tadpole
5. iMpact of gurdon’s research
Gurdon’s experiments captured the attention of
the scientific community
Tools and techniques he developed for nuclear
transfer are still used today
1963- J. B. S. Haldane, in describing Gurdon’s
results, became one of the first to use the word
clone in reference to animals
6. 1964:
F.C. Steward cloned Carrot
1969: First gene isolation
1972: First recombinant DNA molecule
1977: Mouse
1983:
Nuclear transfer
7. 1984:
Steen Willadsen
Cloned a sheep from embryo cells
1986:
Nucleus of an adult cell can also be used
1996:
Ian Wilmut
Villainous sheep "Dolly"
8. Types of Cloning
Cloning is of three types which are as follows
(1) Recombinant DNA technology or DNA
cloning
(2) Reproductive cloning
(3) Therapeutc cloning
9. Recombinant DNA
technology or DNA cloning
DNA cloning, Molecular cloning, Gene cloning
The production of exact copies (clones) of a
particular gene or DNA sequence using genetic
engineering techniques.
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13. Reproductive Cloning
Technology to produce a genetically identical
organism or an animal with the same nuclear
DNA as an existing, or even an extinct, animal.
An embryo is produced through the removal
and transfer of nuclear material in a cell, and the
use of a growth medium
to manipulate that cell
into undergoing mitosis.
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16. Cloning animals for
research
Cloning endangered
species
In order to expand
population
Cloning extinct species
To research their behavior
and other characteristics
18. Therapeutic Cloning
Embryo cloning
Nuclear transplantation of a patient’s own cells
to make an oocyte from which immune-
compatible cells (especially stem cells) can be
derived for transplant.
Not cloned humans or animals
Stem cells harvested at the stage of blastocyst
19. How is Therapeutic Cloning
Performed?
Somatic Cell Nuclear Transfer
Somatic cell
Nuclear
Transfer
20.
21. SCNT Process (1)
Remove the nucleus
from an unfertilized
egg cell (A).
(Done under a
microscope.)
Suction pipette (B)
Glass needle (C)
22. SCNT Process (2)
Gently push the glass
needle through the
tough shell that
surrounds the egg cell.
23. SCNT process (3)
The egg cell’s nucleus
(A) has been released
outside of the egg.
What remains is an
“enucleated” egg (B).
24. SCNT process (4)
•Inject the nucleus (at arrow)
from a donor cell into the
enucleated egg cell.
• Ease the tip of the glass
needle deep into the
enucleated egg cell.
Then, deposit the donor
nucleus.
25. SCNT process (5)
After completing the
nuclear transfer, the
unfertilized egg cell is
“activated” using a
chemical or electrical
treatment that
stimulates cellular
division.
26. SCNT process (6)
The proliferating cells
form a structure called a
blastocyst within days. It
is roughly the same size
as the egg cell.
The right-hand image shows
the blastocyst “hatching”
27. Difference B/W
Fertilization & SCNT
Fertilization = two set of chromosomes
one from sperm and one from egg
SCNT = two set of chromosomes
both from somatic cell as egg’s nucleus has
been removed
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31. 3 goals of therapeutic
cloning by SCNT in humans
Use embryo as source for ES cells
Use ES cells to generate an organ
In this case the organ generated will carry cells
with the same genetic markers as the patient
(recipient)
Correct genetic error in ESC in blastula stage
32. What Are Stem Cells?
Stem cells are the raw material from which
all of the body’s mature, differentiated cells
are made. Stem cells give rise to brain
cells, nerve cells, heart cells, pancreatic
cells, etc.
33. Special characteristics
of ALL stem cells
Self-renewal (proliferation)- the ability of a
stem cell to clone itself indefinitely by cell
division.
Relocation and Differentiation are abilities of
stem cells to “migrate” to where they’re
needed in the body and specialize into a
particular type of mature cell
34. What’s so special about
Stem Cells?
They have the potential to replace cell tissue
that has been damaged or destroyed by severe
illnesses.
They can replicate themselves over and over
for a very long time.
Understanding how stem cells develop into
healthy and diseased cells will assist the search
for cures.
35. Two Kinds of Stem Cells
Embryonic (also called “pluripotent”) stem
cells (ESC) are capable of developing into all the
cell types of the body.
Adult stem cells are less versatile and more
difficult to identify, isolate, and purify.
Stem cells have been found in the blood, bone
marrow, liver, kidney, cornea, dental
pulp, umbilical cord, brain, skin, muscle, salivary
gland .
43. Practical Issues
Some immune rejection may occur- WHY?
About 1% of the DNA in the clone will NOT
be identical to donor cell (patient)
It will be identical to egg cell used in SCNT
REASON: mitochonrial DNA in eggs
Human mitochondria carry about 13
genes, some of which code for surface
proteins
44. Large number of eggs needed for SCNT
To harvest large number of eggs:
Excessive hormone treatment of females
Surgery to retrieve eggs
Both can be harmful to female human
Cow/pig females may be used
Cow/pig eggs will carry species-specific
mitochondrial genes
Steadiness of stem cells