DNA TECHNOLOGY: Part 1
Cloning & Stem Cell Research
Nova video
What is a stem cell?
•Embryonic stem cell – An undifferentiated cell derived from
embryos that have been fertilized in vitro and then donated for
research. Not derived from eggs fertilized in a woman’s body.
•Adult stem cell – An undifferentiated cell found in a
differentiated tissue that can give rise to all the specialized cell
types of the tissue from which it originated. Not controversial.
•Undifferentiated cells are not yet specialized – they can
become different types of cells.
Not all stem cells are created equal
•Totipotent stem cells – can give rise to all types of tissue, i.e. an
embryo
•Pluripotent stem cells – can give rise to most, but not all, tissues of
an organism, i.e. inner mass cells
•Multipotent stem cell – give rise to cells that have a specific
function, i.e. blood stem cells
*Potency = ability to differentiate
What is a
blastocyst? Is
a blastocyst a
human?
Princeton University
University of Wisconsin-Madison
Where do stem cells come from?
 Human embryos (embryonic)
 In Vitro Fertilization (IVF) since late 70s
 Currently 4 million IVF babies alive
 Often creates extra embryos (~400,000
unregulated frozen embryos in U.S.)
 Somatic cells (adult)
 Cells are “reprogrammed” to be
pluripotent
What’s cloning and how is it related?
• Therapeutic cloning (stem cell therapy)Duplicating part of a person/organism e.g. a
heart or liver, or even just a few cells.
• Reproductive cloning- Duplicating an
organism e.g. identical twins.
•Therapeutic cloning can
be patient-specific (cells
from patient put in
donated egg)!
•Resulting cells would be
a perfect match
•Could treat many
diseases (i.e. diabetes) as
body would not reject
cells as foreign
•Experts warned that
there was a risk the cells
could become cancerous.
Are there Human Clones?
•Natural twins - just after fertilization a zygote divides into a twocelled embryo. Each cell continues to divide, producing 2 individuals.
•According to new research, though identical twins share very similar
genes, they ARE NOT identical (environmental & epigenetic factors)
•Epigenetic (chemical) markers that turn genes on and off. Accumulate
due to diet, smoking, etc. Can cause diseases like cancer and influence
behavioral traits
Artificial Twins: Artificial Embryo Twinning
• Occurs in a Petri dish instead of in the mother's body.
• Manually separating an early embryo into individual
cells, and then allowing each cell to divide and
develop
http://www.abpischools.org.uk/resources/poster-series/images/clon02.png
Artificial Twins: Somatic Cell Nuclear Transfer
• Different approach than artificial embryo twinning,
but it produces the same result: an exact clone of an
individual.
(Roslin Institute http://www.roslin.ac.uk/library/)
The SCNT Animal Clone: Dolly
•Nucleus of a sheep’s egg with the
nucleus of a cell from a sheep’s
udder.
•SCNT produces live offspring less
than 1 in every 100 attempts
•Dolly was born in 1996 and
euthanized in 2003 after developing
progressive lung disease
•Agricultural value
(Roslin Institute http://www.roslin.ac.uk/library/)
Cloning & Stem Cell News
•
•
•
•
•
•
•
•
•
•
•
1996 – Dolly born
1998 – First experiment with human stem cells
2001 – Bush restricts federal funding for embryonic stem-cell research
2002 – First cloned cat
2004 – Researchers grow stem cells from embryos using private funding
2005 – South Koreans exposed for lying about creating 1st human clone
2006 – Scientists discover method to extract stem cells without
destroying embryo (this may skirt “when does a human become a
human” issue)
2007 – Human skin cells transformed into cells that look and act like
embryonic stem cells (however, process may cause increased risk of
cancer)
2007 – A mouse was cured of sickle cell anemia using stem cells
2009 – Obama overturns stem cell ban & offers federal funding for
embryonic stem cell research, but opposes human cloning
2009 - Frozen skin used to clone a subspecies of ibex that went extinct in
2000 (Jurassic Park is still not a reality – no appropriate surrogate mothers
for long-dead species)
In small groups generate two lists:
1. The potential uses and benefits of cloning
(therapeutic and reproductive)
2. The potential problems and arguments against
cloning (therapeutic and reproductive)
– Use your notes from the video and be
prepared to share with the class
Potential uses and benefits of cloning
(cells and organisms)
• Replacing organs and other tissues
• Treat a variety of conditions (Parkinson's disease,
burns, heart disease, diabetes, arthritis, etc.)
• Understanding what causes cells to become “sick”
• Infertility
• Replacing a lost child
• Creating donor people
• Gene therapy
• Saving endangered species
Problems/arguments against cloning
(cells and organisms)
•
•
•
•
•
•
•
Low success rate (Dolly took 276 attempts)
Tumors & genetic defects
Pre-mature aging (genetic age)
Massive quantities of human eggs required
Less genetic variation
Lack of knowledge
Value of life (blastocyst)