MadSci Network: Genetics

Re: How will cloning help us in the future and how did it help in the past.

Date: Thu Feb 8 14:19:12 2001
Posted By: Christopher Carlson, Senior Fellow, Dept. of Molecular Biotechnology
Area of science: Genetics
ID: 980220632.Ge

Hi Young,

	Before I answer your question, I recommend that you take a look at the
madsci website, where
you will find that the
qualification for participating in MadSci is "Knowledge of a particular
area of science and a willingness to communicate your expertise with
others."  If you look at the list of participating scientists for any area
at MadSci (
) you will see a breadth
of background from undergraduates through full faculty members and
everything in between.  We aren't necessarily world renowned leaders in our
field; we are simply individuals with a better than average background in
our favorite fields, willing to do our best at answering scientific
questions submitted from the larger community.

	I happen to hold a Ph.D in genetics from Stanford University, but I am not
actively involved in cloning research.

	Now to your question: how did cloning help us in the past?  First I want to
discuss the meanings of "cloning".   More than two decades ago it became
possible to splice together bits of DNA and replicate the spliced product.
 This process has become known as cloning, based on the fact that once a
specific bit of DNA is spliced into a vector it may be replicated as many
times as you want.  This type of cloning revolutionized the world of
molecular biology, allowing us to easily perform tasks as diverse as
production of enzymes from cloned genes, sequencing of cloned DNA, and even
mapping the human genome using large libraries of clones which each contain
a small portion of the overall genome.

	However, I suspect that you didn't actually mean cloning in that sense.  The
meaning of cloning which is more prominent in the media today is the
duplication of an organism using the same genetic blueprint.  While it
certainly made a splash when "Dolly" the sheep was cloned, natural clones
have existed since the dawn of time: in many organisms (bacteria and many
fungi come to mind) there is no sex, and all offspring are genetically
identical to their parents.  In higher organisms (plants and animals) it is
more common to reproduce sexually, although there are some interesting
exceptions to the rule.

	For example, in reptiles sex is not determined by an X and Y chromosome, but
by the temperature at which the eggs incubate.  Higher temperatures
generally produce females.  In desert regions many species of lizard have
been identified in which all eggs develop as females.  For a sexually
reproducing organism this would have rather disastrous results within one
generation, but these lizards are capable of reproducing clonally.  All
daughters are clones of their mother.  While this is certainly an
interesting adaptation to an environment with rising temperatures, it
hasn't really helped "us" much.

	So how has cloning of mammals helped us?  The field is new enough that most
Americans haven't yet experienced any remarkable improvements in their lot
from cloning, but this may soon change.  The field where cloning has
originated is agriculture, where one of the challenges since we first
domesticated animals has been to create livestock which are more productive
(more meat, more milk, more fur, etc.)  The greatest challenge has been to
create breeds of livestock which reliably transmit productive
characteristics.  As a result, we've got Hereford cattle (which have high
muscle mass) and Jersey cattle (which produce large amounts of milk).
These breeds do have higher levels of production on average, but there is
still significant variation within breed.

	If you've ever been to a rural county fair, you've seen the judging
competitions for livestock.  What if you could just clone the prizewinning
livestock and avoid the messiness of  breeding for the best possible
combination of traits?  The practice of cloning isn't yet reliable enough
to produce herds of identical super livestock more efficiently than doing
it the old fashioned way by breeding the prizewinners.  On the other hand,
it is possibly a more efficient way to expand herds of genetically altered
livestock, which have been created to produce therapeutic proteins in their

	In the meantime, cloning has helped us understand some of the basic biology
of aging and cellular differentiation.  One of the models for aging held
that the length of structures at the end of chromosomes known as telomeres
is one of the clocks regulating the aging of an organism.  Older cells do
have shorter telomeres.  However, the fact that we can experimentally
reverse this process in clones suggests that the shortening of telomeres is
not the simple, inexorable process we thought it was.  This remains one of
the hottest areas of cloning research.

	The revolution of nuclear transfer technologies is that if you take a
nucleus out of a cell from a somatic tissue of a fully grown organism you
can reprogram it to behave as if it were the nucleus of an undifferentiated
fertilized egg.  This has fascinating implications for producing
replacement tissues: some organs like the liver are capable of
regeneration, while most other organs cannot.  What if we could grow a new
kidney for people who need one?  If we can take a fully differentiated cell
all the way back to an undifferentiated state where it can grow into an
entire organism, perhaps we can reprogram it to grow into a kidney.
Thousands of people die every year waiting for tissue matched donor organs,
so if we can figure out how to artificially produce replacement organs
through a process similar to cloning, we could save thousands of lives per

	I hope this begins to answer your question.

	Chris Carlson

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