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Cloning
Christopher Thompson
Part 1:What is cloning?
What exactly is cloning?
• Cloning is the creation of an organism that is an exact genetic copy
of another. This means that every single bit of DNA is the same
between the two!
• You might not believe it, but there are human clones among us right
now. They weren't made in a lab, though: they're identical twins,
created naturally. Below, we'll see how natural identical twins relate
to modern cloning technologies.
How is cloning done?
• You may have first heard of cloning when Dolly the Sheep showed
up on the scene in 1997. Cloning technologies have been around for
much longer than Dolly, though.
• How does one go about making an exact genetic copy of an
organism? There are a couple of ways to do this: artificial embryo
twinning and somatic cell nuclear transfer. How do these processes
differ?
Part 2 What is cloning?
Is cloning an organism the same as cloning a gene?
• You've heard about cloning animals - sheep, mice, even house pets
- in the news. From time to time, you may have also heard about
researchers cloning, or identifying, genes that are responsible for
various medical conditions or traits.
What is the difference?
• Cloning an animal, or any other organism, refers to making an exact
genetic copy of that organism. The techniques used to clone
organisms are described on this page.
• Cloning a gene means isolating an exact copy of a single gene from
the entire genome of an organism. Usually this involves copying the
DNA sequence of that gene into a smaller, more accessible piece of
DNA, such as a plasmid. This makes it easier to study the function
of the individual gene in the laboratory.
Part 3 What is cloning
How does SCNT differ from the natural way of making an embryo?
• The fertilization of an egg by a sperm and the SCNT cloning method
both result in the same thing: a dividing ball of cells, called an
embryo. So what exactly is the difference between these methods?
• An embryo is composed of cells that contain two complete sets of
chromosomes. The difference between fertilization and SCNT lies in
where those two sets originated.
• In fertilization, the sperm and egg both contain one set of
chromosomes. When the sperm and egg join, the resulting zygote
ends up with two sets - one from the father (sperm) and one from
the mother (egg).
• In SCNT, the egg cell's single set of chromosomes is removed. It is
replaced by the nucleus from a somatic cell, which already contains
two complete sets of chromosomes. Therefore, in the resulting
embryo, both sets of chromosomes come from the somatic cell.
Part 1 Click and Clone
• Step !: Isolate donor cells
• Step 2: Remove and discard the nucleus
from the egg cell
• Step 3: Transfer the somatic cell nucleus
into the enucleated egg cell
• Step 4: Stimulate cell division
• Step 5: Implant the embryo
• Step 6 : Deliver
Part 1 Clone zone
• 1928- It’s true: The nucleus is in charge
• 1952- Frogs galore! Nuclear transfer
becomes a reality
• 1968- For cloning. Any nucleus will do
• 1975- Cloning with a wee wittle wabbit egg
• 1996- Hello, Dolly
• 1997- Promises and pitfalls of human
cloning
Part 1 Why Clone
1. Cloning for medical purposes
•
Of all the reasons, cloning for medical purposes has the most potential to benefit large numbers of
people. How might cloning be used in medicine?
Cloning animal models of disease
•
Much of what researchers learn about human disease comes from studying animal models such
as mice. Often, animal models are genetically engineered to carry disease-causing mutations in
their genes. Creating these transgenic animals is a time-intensive process that requires trial-anderror and several generations of breeding. Cloning technologies might reduce the time needed to
make a transgenic animal model, and the result would be a population of genetically identical
animals for study.
Cloning stem cells for research
•
Stem cells are the body's building blocks, responsible for developing, maintaining and repairing
the body throughout life. As a result, they might be used to repair damaged or diseased organs
and tissues. Researchers are currently looking toward cloning as a way to create genetically
defined human stem cells for research and medical purposes. To see how this is done, see
Creating Stem Cells for Research, a component of the Stem Cells in the Spotlight module.
"Pharming" for drug production
•
Farm animals such as cows, sheep and goats are currently being genetically engineered to
produce drugs or proteins that are useful in medicine. Just like creating animal models of disease,
cloning might be a faster way to produce large herds of genetically engineered animals. Find out
more about this research in the feature article
Part 1 Clone Myths
Misconception #1: Instant Clones!
• Let's say you really wanted a clone to do your homework. After
reviewing What is Cloning? and Click and Clone, you've figured out,
generally, how this would be done. Knowing what you know, do you
think this approach would really help you finish your homework...this
decade?
• A common misconception is that a clone, if created, would magically
appear at the same age as the original. This simply isn't true. You
remember that cloning is an alternative way to create an embryo,
not a full-grown individual. Therefore, that embryo, once created,
must develop exactly the same way as would an embryo created by
fertilizing an egg cell with a sperm cell. This will require a surrogate
mother and ample time for the cloned embryo to grow and fully
develop into an individual
Part 2 Clone Myths
Misconception #2: Carbon Copies!
• Your beloved cat Frank has been a loyal companion for years. Recently, though,
Frank is showing signs of old age, and you realize that your friend's days are
numbered. You can't bear the thought of living without her, so you contact a
biotechnology company that advertises pet cloning services. For a fee, this company
will clone Frank using DNA from a sample of her somatic cells. You're thrilled: you'll
soon have a carbon copy of Frank - we'll call her Frank #2 - and you'll never have to
live without your pal! Right?
• Not exactly. Are you familiar with the phrase "nature versus nurture?" Basically, this
means that while genetics can help determine traits, environmental influences have a
considerable impact on shaping an individual's physical appearance and personality.
For example, do you know any identical twins? They are genetically the same, but do
they really look and act exactly alike?
• So, even though Frank #2 is genetically identical to the original Frank, she will grow
and develop in a completely different environment than the original Frank or will have
a different mother, and she will be exposed to different experiences throughout her
development and life. Therefore, there is only a slim chance that Frank #2 will closely
resemble the Frank you know and love.
Part 3 Clone Myths
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The answer lies on the X chromosome. In cats, a gene that helps determine coat color resides on
this chromosome. Both CC and Rainbow, being females, have two X chromosomes. (Males have
one X and one Y chromosome.) Since the two cats have the exact same X chromosomes, they
have the same two coat color genes, one specifying black and the other specifying orange.
So why do they look different?
Very early in her development, each of Rainbow's cells "turned off" one entire X chromosome and therefore, turned off either the black color gene or the orange one. This process, called Xinactivation, happens normally in females, in order to prevent them from having twice as much Xchromosome activity as males. It also happens randomly, meaning that not every cell turns off the
same X chromosome.
As a result, Rainbow developed as a mosaic of cells that had one or the other coat color gene
inactivated - some patches of cells specified black, other patches specified orange, and still others
specified white, due to more complex genetic events. This is how all calico cats, like Rainbow, get
their markings.
CC looks different because the somatic cell that Rainbow donated to create her contained an
activated black gene and an inactivated orange gene. What's interesting is that, as CC developed,
her cells did not change that inactivation pattern. Therefore, unlike Rainbow, CC developed
without any cells that specified orange coat color. The result is CC's black and white tiger-tabby
coat.
Rainbow and CC are living proof that a clone will not look exactly like the donor of its genetic
material.