IB Biology Year 1, IHS
STEM CELLS and CLONING KEY
Directions: After reading 20.3 from Neil 9e, “Cloning organisms may lead to production of stem cells…” and watching the 6 stem
cell animations online at http://www.stemcellresearch.umich.edu/overview/tutorial.html , answer the following in your journal.
1. Give an example of a differentiated cell and an undifferentiated cell.
A differentiated cell is one that is expressing only some of its genes. A kidney cell is
an example of a differentiated cell. Cells of early stage embryos are undifferentiated.
2. Carrots and frogs were cloned in the 1950’s; “Dolly” the sheep was cloned in the late
1990’s. After studying figures 20.17, 20.18 and 20.19, make a labeled generic diagram
called “How to Clone.” See second page.
3. What does cloning have to do with stem cells?
If someone wanted to produce stem cells that a patient would not reject, s/he would
take the nucleus from a patient’s cell and put it into an enucleated egg cell. Then, the egg
cell with the donated nucleus would be made to divide, producing an embryo. This is as far as the procedure would
go because the embryo would be sacrificed to obtain the compatible stem cells for treatment, but it would
theoretically be possible to implant the embryo into a surrogate uterus. If the implantation was successful and
the pregnancy resulted in a baby, that baby would be a clone of the patient.
4. Describe the two key features of stem cells.
They can both reproduce themselves indefinitely and, under appropriate conditions, be made to differentiate
into specialized cells of one or more types.
5. Compare the capabilities of human embryonic stem cells (hES cells) vs. human adult stem cells.
hES cells hold more promise than adult stem cells for most medical applications because hES cells are pluripotent,
capable of differentiating into many different cell types. Adult stem cells are not able to give rise to all cell types in
the organism. For example, stem cells in bone marrow can generate all the different kinds of blood cells. Adult
stem cells are not as versatile as embryonic stem cells.
6. From what source do researchers obtain hES cells?
hES cells are obtained from leftover 4 to 5-day old embryos donated by patients who underwent infertility
treatment. Not every embryo produced by in vitro fertilization can be implanted into a woman. A survey by the
RAND corp. was sent to every assisted reproductive technology facility in the United States... The results showed
that as of April 11, 2002, a total of 396,526 embryos had been placed in storage in the United States.
7.
How could scientists prevent the immune system of a patient undergoing stem cell therapy from rejecting the
donated stem cells?
Somatic cell nuclear transplantation (SCNT): with a donor nucleus from a person with a particular disease, they
might be able to produce ES cells for treatment that match the parent and are thus not rejected by his or her
immune system.
8. What are iPS cells?
iPS or induced pluripotent stem cells were first made in 2007. Researchers put four “stem cell master regulatory
genes” into adult cells, which appeared to reprogram those adult cells to act like ES cells. iPS cells created in this way
could eventually provide tailor-made replacement cells for patients without using human embryos, sidestepping
ethical objections. However, more research is needed to know whether iPS cells have the same potential as ES cells.
9,
Explain why someone might be opposed to developing medical treatments that use hES cells. Explain why
someone might be in favor of them.
Someone opposed to developing treatments that use hES cells might feel that it is unethical to kill one human
being. Others might feel that an IVF clinic human embryo is not a human being, but a rather, a group of cells that
has the potential to save human beings.