Title: Clones in animals
Homework: learning package 11 due in today
Ewe were
always on
my mind….
Learning Outcomes
(e) describe how artificial clones of animals can
be produced;
(f) discuss the advantages and disadvantages of
cloning animals (HSW4, 6a, 6b, 7c).
Stem Cells
• All cells start of with the same
DNA, so why do they end up
looking so different?
• Some genes “switch on” while
others “switch off”, leading to a
process called differentiation.
• Cells that have differentiated
cells lose their ability to divide
and produce more cells of
different kinds.
Stem Cells
• What happens to cells that
remain undifferentiated?
• These undifferentiated cells
are called stem cells – they
have the ability to become
any other cell in the body
(or more stem cells).
• Why is this useful?
Obtaining stem cells - embryos
• Most useful at a few days
old – ball of undifferentiated
cells.
• Cells at this stage are
totipotent – divide to form a
whole new organism!
• 50-100 cell stage is
described as pluripotent –
ability to become any cell
type, but not a new
organism because some cell
differentiation has already
started.
Stem cells
Embryonic stem
cells
Totipotent cells
can divide to
form a new
organism
Pluripotent cells can
divide to form any
other specialised cells
of any type
Embryo formation
• Embryo is formed by transferring DNA from
embryonic stem cells to an egg whose nucleus
has been removed (enucleated).
• Reconstructed egg containing DNA from a
donor cell is treated with an electric current to
stimulate cell division and blastocyst
formation.
Cloning by nuclear
transfer
Cloning by splitting
embryos
What are the differences between cloning by splitting of
embryos and cloning by nuclear transfer?
Splitting of embryos
•
•
•
•
The nucleus comes from an egg
fertilised in vitro and allowed to
divide to form an embryo
The embryos produced are
clones of the original zygote
The zygote is a product of a
fertilised egg. Since this is
formed from fusion of sperm and
egg cells which are themselves a
product of meiosis, it is
impossible to know exactly what
characteristics the cloned
organism will possess
All cellular components are
derived from the original zygote.
The mitochondrial DNA
component will be identical in
each clone
Nuclear transfer
– The nucleus comes from an adult,
differentiated cell taken from the animal
to be cloned
– The embryos produced are clones of the
donor adult organism
– The adult cell is a product of an adult
with known characteristics. It is
therefore known what characteristics
the clones will possess
– The cellular components are derived
from the egg cell used therefore the
mitochondrial DNA component will be
different from that of the original adult
cell
Reproductive vs non-reproductive
• Reproductive cloning
– Cloning to produce a
whole organism
– Examples
• Embryo transplantation
• Dolly the sheep
• Non-reproductive
cloning
– Using cloning to produce
cells
– Examples
• Stem cell research
• Production of cells,
tissues or organs
Dolly the Sheep
• Dolly the sheep is
believed to have
suffered from a serious
health problem which
developed at a
relatively early age
Non-reproductive cloning in animals
• Non-reproductive cloning involves the production of
genetically identical cells
– 1951 – HeLa cells
• Cancerous cells which divide repeatedly in culture solution
• Used in medical research
– Stem cells
• Totipotent or pluripotent
• Undifferentiated cells that are able to differentiate into specialised
cells
• Embryonic stem cells – ethical arguments
Possibilities of non-reproductive cloning
• Potential future uses include
– Regeneration of heart tissue
following a heart attack
– Repair of nervous tissue
– Repairing the spinal cord
• Stem cells taken from the patient
to produce the tissues mean that
tissue rejection by the immune
system is less likely
Advantages and disadvantages of
cloning animals
Advantages
Disadvantages
High-value animals, for example cows
giving high milk yield, can be cloned in
large numbers
High-value animals are not necessarily
produced with animal welfare in mind.
Some strains of meat-producing chickens
have been developed that are unable to
walk
Rare animals can be cloned to preserve
the species
As with plants – excessive genetic
uniformity in a species makes in unlikely
to be able to cope with, or adapt to,
changes in the environment
Genetically modified animals – for
example sheep that produce
pharmaceutical chemicals in their milk –
can be quickly reproduced
It is still unclear whether animals cloned
using the nuclear material of adult cells
will remain healthy in the long term.
Dolly was put down at 6 years old due to
lung cancer caused by a virus, although
post-mortem showed nothing unusual
Artificial Cloning in animals
• Advantages
– High value animals
– Rare animals can be
cloned
– Quickly reproduced
• Disadvantages
– Animal welfare
– Genetic uniformity, loss
of genetic variation
– Uncertainties of health
of cloned animals
Moral and ethical Arguments

Is it right to clone an aging pet?

Is it right to clone an animal which leads to a
cure for human diseases?
Give reasons why repairing a damaged heart using
cloned cells could potentially be less dangerous than
receiving a heart transplant
• Heart transplant surgery carries with it risk of infection associated with
any major surgery.
• There are also risks associated with use of general anaesthetic.
• The transplanted heart is foreign tissue – as such it may be rejected by the
host’s immune system.
• Cloned cells are derived from the host and it may be possible to get them
to the right location using relatively minor surgical methods