Title |
How Does Cloning Work? |
Time Required |
Preparation Time:
15 minutes Class Time:
10-15 minutes |
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Objectives |
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·
To
teach students how cloning works technically. ·
To
use students’ existing biology knowledge and apply it to cloning. |
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Preparation Materials |
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Background In the 1920s, Hans
Spemann first explored nuclear transfer in order to conduct genetic
research. Currently, all animal
cloning experiments use a variation of nuclear transfer. Using sheep as an example, this is how
nuclear transfer works: 1. Nuclear transfer involves two cells: an egg
cell and a donor cell. The egg cell
should be unfertilized—because it is more likely to accept the donor cell’s
nucleus as its own—and enucleated—which eliminates the majority of its
genetic information. 2. The donor cell—which provides all the genetic information for
the clone—is forced into the Gap Zero
cell stage, which causes the cell to shut down but not die. 3. The two cells are then fused together with an electrical
pulse. This step simulates
fertilization of the egg by sperm. The few surviving electrically-activated
cells form to produce an embryo. 4. If the embryo survives, it is allowed to grow for six days and
is incubated in a sheep’s oviduct. Embryos placed in oviducts are found much
more likely to survive than those placed in test tubes. 5.
The embryo is then placed in the uterus of
the surrogate
mother ewe. The ewe carries
the embryo until birth. 6.
The surrogate mother ewe gives birth to the
clone, which is an exact copy of the donor animal. The newborn will have all the same characteristics of any other
normal newborn sheep. Vocabulary List Egg – This is the female reproductive cell. This cell provides half of the genetic
makeup and, after fertilization, develops into an embryo. Gap Zero
cell stage – This stage in the cell cycle is
the dormant phase. During cloning,
the donor cell needs to be in this stage in order to accept the egg cell. Sperm
- This is the male reproductive cell. This cell provides half of the genetic
makeup to an egg at the time of fertilization. Embryo - The stage of prenatal development after fertilization. In
humans, it is followed by the fetus stage and then birth. In animals, it is
the only stage before birth. Oviduct
– The tube in which an egg cell is
fertilized and resides in until it travels into the uterus for implantation.
Also known as the fallopian tube. Surrogate
mother – An organism
used to carry and give birth to embryos which are not its own. Online Resources Think Quest
– Cloning techniques |
Resources |
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How Does Cloning Work? slides (here) Computer with Microsoft PowerPoint Overhead projector |
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Procedure |
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Use the How Does Cloning Work? slides
to teach students, step-by-step, how to clone a sheep. |