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Chapter 21
Cloning
Cloning
 Using the somatic cells of a multicellular
organism to generate a new organism
is called cloning. Each clone is
genetically identical to the parent plant.
 Differentiated cells don’t usually divide
in culture, so researchers had to take a
different approach to decide if animal
cells were totipotent.
What Researchers Did…
 They removed the
nucleus of an unfertilized
egg and replaced it with
one from a differentiated
cell.
 The process is called
nuclear transplantation.
 If the transplanted cell
retains all of its genetic
information, the recipient
cell should develop with
all of the necessary
tissues and organs.
Nuclear Transplantation
 As these experiments
were conducted on frogs,
it was determined that
something in the DNA
does change.
 In tadpoles, normal
development proceeded,
but as the age of the
donor nucleus increased,
the percentage of
organisms that developed
correctly decreased.
Nuclear Transplantation
 Continued research showed that the
DNA remains the same for the most
part, but the chromatin changes in a
way that problems arise.
Nuclear Transplantation
 Often times, the histones get modified or
DNA is methylated and these changes in the
chromatin prevent dedifferentiation.
 Sometimes the process is reversible, but
usually it isn’t. One thing is certain, most
scientists agree that all cells contain the
necessary genetic information to make an
entire organism. However, the different cell
types exist because of the variations in gene
expression.
Nuclear Transplanting and
Cloning
 In 1997, Scottish researchers cloned a
sheep named Dolly.
 They used cells from mammary tissue
in an adult sheep, implanted the
nucleus from the cell into egg cells from
which the nucleus had been removed
and implanted into the uterus of a
lamb.
Nuclear Transplanting and
Cloning
 Analysis of the DNA from Dolly showed
it was identical to that of the original
sheep, and its mitochondria matched
that of the mother lamb.
 However, Dolly’s cells appeared older
than her age would indicate.
Dolly’s Problems
 She suffered from a lung disease seen
in older sheep.
 She had arthritis.
 These results indicate that not all of the
DNA had been reprogrammed.
Problems With Animal Cloning
In General:
 Many of the animals exhibit a variety of
defects such as obesity and premature death.
 Only a small percentage of the embryos
created develop correctly resulting in live
birth.
 Possible reasons for these results include:
 Epigenetic changes in chromatin (acetylation of
histones and/or methylation of DNA) result in only
a small number of genes being turned on while
the others remain suppressed.
Cloning
 Many plant species and some animal
species have natural methods of
cloning.
Rotifers
Strawberries
Potatoes
Amoeba
Hydra
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Rotiers
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Rotifera
 Rotifers are tiny, microscopic
animals inhabiting fresh water,
marine, and damp soil.
 Unique because many of them
reproduce via parthenogenesis.
Parthogenesis
 With parthenogenesis, females produce
offspring from unfertilized eggs.
Parthogenesis
 Some species of rotifers produce two
types of eggs.
 One develops into a female, the other
into a short-lived male.
 The male survives long enough to
produce sperm that fertilize the eggs.
Parthogenesis
 Some rotifers produce females.
 These females lay more unfertilized
eggs that develop into more females.
Runners
 Strawberry plants reproduce asexually
through their stolons. These stolons
are commonly referred to as “runners.”
 Stolons are stems that grow along the
ground or just below it and produce
nodes.
 Stolons periodically produce nodes that
can grow roots.
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Runners
 The nodes occasionally give rise to
roots.
 If roots grow, a new plant will grown
and later produce strawberries.
 The daughter plants are clones of the
original.
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Tubers
 Tubers such as
potatoes form enlarged
stolons.
 The enlarged stolons
develop into storage
organs that store
nutrients for the
formation of a new
plant the following year.
http://www.potatoes.co.nz/Potato_know_how/
Tubers
 The tubers have
multiple eyes that each
generate shoots that
can grow into new
plants when conditions
are favorable.
 All plants propagated
from the same tuber
are clones of the
parent.
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http://www.potatoes.co.nz/Potato_know_how/
Budding
 Budding is a form of
asexual reproduction in
which a new organism
develops from a bud of
the original cell.
 Yeast are fungi that can
reproduce by budding.
 Each new cell that buds
off is a clone of the
original.
http://en.wikipedia.org/wiki/Budding#/media/File:S_cerevisiae_under_DIC_microscopy.jpg
Budding
 Corals, sponges and
hydra are common
animals that
reproduce by
budding.
 Each bud is a
descendent of the
original and is a
clone.
http://en.wikipedia.org/wiki/Budding#/media/File:Hydra_oligactis.jpg