Neurodevelopmental disorders according to the dsm 5 tr
Cloning
1. Cloning
Dr. Radhakrishna G Pillai
(MSc (KU), MSc (London), Ph.D, LLB, BEd, PGCE (London), SLTP (London), PGDDE)
2. What is cloning in biology
• Variable meaning in biology
• Obtaining copies more or less precise of a biological entity
• Three common types of cloning;
– cloning genes
– cloning cells and
– cloning individuals
• Cloning an individual: in case of a multicellular organism, such as a
plant or an animal is not strictly possible
• The genes of an individual, the genome, can be cloned, but
• The individual itself cannot be cloned
3. Cellular Cloning
• Unicellular organisms such as;
– bacteria and yeast
– naturally produce clones of themselves
– During their asexual reproduction
• Known as cellular cloning
• The nuclear DNA duplicates by the process of
mitosis, which creates an exact replica of the
genetic material
5. Human cloning
• Suggested as a way to improve the genetic endowment of
mankind:
– by cloning individuals of great achievement
– for example, in sports, music, the arts, science, literature,
politics, and the like, or of acknowledged virtue
• The clone may not be exact copy phenotypically: never
been taken seriously
• The obstacles and drawbacks are many and insuperable, at
least at the present state of knowledge
• Many advertise that they were ready to carry out the
cloning
6. Cloning genes/cell
• Cloning genes or, more generally,
cloning DNA segments is routinely
done in many genetics and
pharmaceutical laboratories
throughout the world
• Technologies for cloning cells in the
laboratory are seven decades old
and
• Cloning of cells is used for
reproducing a particular type of
cell
• Eg. skin or liver cell: to investigate
its characteristics
7. Natural cloning
• Individual human cloning occurs naturally in the
case of identical twins
• Two individuals develop from a single fertilized egg
• These twins are called identical, precisely because
they are genetically identical to each other
• The sheep Dolly, cloned in July 1996
– the first mammal artificially cloned using an adult
cell as the source of the genotype
• Frogs and other amphibians were obtained by
artificial cloning as early as 50 y earlier
8. Can a human individual be cloned?
• Strictly speaking: No
• What is cloned are the genes, not the
individual; the genotype, not the phenotype
• The technical obstacles are immense even for
cloning a human’s genotype
9. Success rate
• Ian Wilmut Succeeded with Dolly only
after 270 trials
• The rate of success for cloning
mammals has notably increased over
the years but far below 100%
• Presently mice, rats, goats, sheep,
cows, pigs, horses, and other
mammals are cloned
• The great majority of pregnancies end
in spontaneous abortion
• In many cases, the death of the fetus
occurs close to term, with devastating
economic, health, and emotional
consequences
10. Reproductive cloning
• The deliberate production of genetically
identical individuals
• Each newly produced individual is a clone of
the original
• Clones contain identical sets of genetic
material in their chromosomes—of every cell
in their bodies
• Cells from two clones have the same DNA and
the same genes in their nuclei
11. Mitochondrial DNA
• Cells also contain some DNA in the
mitochondria
• Mitochondria contain their own DNA
and reproduce independently
• True clones will have identical DNA in
both the nuclei and mitochondria
• Individuals that have identical
nuclear DNA but different
mitochondrial DNA is also called
clones
12. Cloning using somatic cell nuclear
transfer (SCNT)
• Remove the chromosomes (Nucleus) from an
egg: enucleated egg
• The chromosomes are replaced with a nucleus
from a somatic (body) cell
• Somatic cell from the donor of egg cell or from
another individual
• Cells obtained directly from the individual, cells
grown in culture, or frozen tissue
• Transfer to the uterus of synchronized recipient
mothers
• Carried to term to produce live cloned off-spring
13. SCNT
• The egg is then stimulated and in some cases it starts to divide
• If that happens, a series of sequential cell divisions leads to
the formation of a blastocyst, or preimplantation embryo
• The blastocyst is then transferred to the uterus of an animal
• The successful implantation of the blastocyst result in its
further development, culminating in the birth of an animal
• This animal will be a clone of the individual that was the
donor of the nucleus
• Its nuclear DNA has been inherited from only one genetic
parent
14. Limitations in SCNT
• The number of times that a given individual can be cloned is
limited by the number of eggs that can be obtained
• The number of females available to receive developing embryos
• Approximately 40-50% of the reconstructed embryos develop to a
stage suitable for transfer
• Only about 10% result in the birth of a live cloned calf
• Currently only about 4-5% of cloned embryos originally
constructed actually make it to become calves
15. Inheritance of DNA
• If the egg and somatic cell are from the same individual:
– result an embryo that receives all its genetic material—nuclear
and mitochondrial—from a single individual
• That will also be true if the egg comes from the nucleus
donor's mother: mitochondria are inherited maternally
• Multiple clones might also be produced by transferring
identical nuclei to eggs from a single donor
• If the somatic cell nucleus and the egg come from different
individuals: clone not identical to the nuclear donor as
mitochondrial genes are different
16. Cloning by embryo splitting
• Begins with in vitro fertilization (IVF)
• The zygote divides into two and then
four identical cells
• Separate the cells and allowed to
develop into separate but identical
blastocysts
• Implant the blastocyst in a uterus
• Limited developmental potential
• Embryo splitting can yield only two
identical and probably no more than
four identical individuals
17. Similarity in DNA
• The DNA in embryo splitting is contributed by
germ cells from two individuals
• Thus, the embryos, like those formed naturally
or by standard IVF, have two parents
• Their mitochondrial DNA is identical
• This method of cloning is identical with the
natural formation of monozygotic twins
18. WILL CLONES LOOK AND BEHAVE THE SAME?
• Clones are genetically identical with one another
• They will not be identical in physical or behavioral
characteristics
• DNA is not the only determinant of these
characteristics
• A pair of clones will experience different environments
and nutritional inputs while in the uterus,
• Subjected to different inputs from their parents,
society, and life experience as they grow up
19. Differences in phenotype of clones
• Clones with identical nuclear and identical
mitochondrial DNA
– but born at different times
– the environmental and nutritional differences
– would be expected to be more pronounced than for
monozygotic (identical) twins
• Monozygotic twins may not be fully identical
genetically or epigenetically:
– mutations, stochastic developmental variations, and
varied imprinting effects (parent-specific chemical marks
on the DNA) make different contributions to each twin
20. Mitochondrial DNA
• Clones that do not have identical mitochondria are
genetically different
• Such clones arise if one individual contributes the
nucleus and another the egg
• Nuclei from a single individual transferred to eggs from
multiple donors are also genetically different
• The differences in mitochondrial DNA might be
expected to show up in parts of the body that have
high demands for energy
– such as muscle, heart, eye, and brain or
– in body systems that use mitochondrial control over cell
death to determine cell numbers
21. Why Reproductive cloning?
• Cloning of livestock is a means of
– replicating an existing favorable combination of traits, such as efficient
growth and high milk production
– exclude the impact of genetic “lottery” and
– mixing that occur in sexual reproduction
• It allows an animal with a particular genetic modification, such as
the ability to produce a pharmaceutical in milk, to be replicated
more rapidly than does natural mating
• Moreover a genetic modification can be made more easily
– genetic modifications in cultured cells and
– the modified cell nucleus transferred to an enucleated egg to make a
clone
• Mammals used in scientific experiments, such as mice, are cloned as
part of research
– To increase our understanding of fundamental biological mechanisms
22. Human reproductive cloning
• People wish to produce children through
reproductive cloning include:
– Individuals who wish to have a child that is genetically
identical with them, or with another nucleus donor
• Infertile couples
– Parents who have lost a child and wish to have another
genetically identical child
– People who need a transplant (Eg. cord blood) to
• treat their own or their child's disease and
• collect genetically identical tissue from a cloned foetus or
newborn
23. Reproductive cloning
• Transplantable tissue may be available without
the need for the birth of a child produced by
cloning
• For example, embryos produced by in
vitro fertilization (IVF) can be typed for transplant
suitability
• In future stem cells produced by nuclear
transplantation may allow the production of
transplantable tissue
24. Stem cells through SCNT
• Somatic cell nuclear transfer or nuclear transplantation (NT):
alternative route to obtaining stem cells that could be used for
transplantation therapies
– with a minimal risk of transplant rejection
• This procedure sometimes called:
– therapeutic cloning/ research cloning or non-reproductive cloning
– would be used to generate pluripotent ES cells
– that are genetically identical with the cells of a transplant recipient
• Avoid/ameliorate the rejection seen with unmatched transplants
• The ES cells from NT have the advantage over adult stem cells
– being able to provide virtually all cell types and
– able to be maintained in culture for long periods of time
• In the future they might be used to generate tissues and,
theoretically, complex organs for transplantation
25. Stem cell therapy through NT
• Transfer of a somatic cell nucleus
from a patient into an enucleated
egg
• in vitro culture of the embryo to the
blastocyst stage and
• Pluripotent ES cell line from the inner
cell mass of this blastocyst
• Derive specialized cells (and, if
possible, tissues and organs) in
laboratory culture for therapeutic
transplantation
26. Stem cells from SCNT
• Could avoid a major cause of
transplant rejection
Possible drawbacks of this
• Presence of divergent
mitochondrial proteins in cells
may create “minor”
transplantation antigens
– that can cause rejection
• Not be a problem: if the egg were
donated by the mother of the
transplant recipient or the
recipient herself
27. Autoimmune diseases
• For some autoimmune diseases, transplantation of cells
cloned from the patient's own cells may be inappropriate
• These cells can be targets for the ongoing destructive process
• In disorder that has a genetic origin: ES cells derived by SCNT
from the patient's own cells would carry the same defect
– Need genetic modification before they could be used for
therapeutic transplantation
• Using another source of stem cells is more likely to be
feasible than
– the challenging task of correcting the one or more genes that are
involved in the disease in adult stem cells or
– in a nuclear transplantation-derived stem cell line initiated with a
nucleus from the patient
28. Uses of stem cells from SCNT
• Therapeutic use
• Used in laboratories for several types of studies in clinical medicine
and for fundamental research in human development
• Such studies could not be carried out with mouse or monkey ES cells
and are not likely to be feasible with ES cells prepared from normally
fertilized blastocysts
– Eg. ES cells derived from humans with genetic
– permit analysis of the role of the mutated genes in both cell and tissue
development and in adult cells difficult to study otherwise.
– Eg nerve cells of the brain
• Disadvantage: it would require the use of donor eggs
• But for the study of many cell types
– there may be no alternative to the use of ES cells
– the derivation of primary cell lines from human tissues is not possible
29. Artificial Embryo Twinning
• Artificial embryo twinning is a relatively low-tech
way to make clones
• This mimics the natural process that creates
identical twins
• In nature, twins form very early in development
when the embryo splits in two
• Twinning happens in the first days after egg and
sperm join
– the embryo is made of just a small number of
unspecialized cells
• Each half of the embryo continues dividing on its
own, ultimately developing into separate,
complete individuals
• From the same fertilized egg: genetically identical
30. Artificial embryo twinning
• Uses the same approach as natural embryo
twinning
• It is carried out in a Petri dish instead of
inside the mother
• A very early embryo is separated into
individual cells, which are allowed to divide
and develop for a short time in the Petri dish
• The embryos are then placed into a
surrogate mother, where they finish
developing
• Since all the embryos came from the same
fertilized egg, they are genetically identical
32. Issues to be resolved
• Birth of Dolly happened only after 270 trials
• The great majority of pregnancies end in spontaneous
abortion
• The death of the fetus occurs close to term
– with devastating economic, health, and emotional consequences in
the case of humans
• In mammals, in general, the animals produced by cloning
suffer from serious health handicaps
– gross obesity
– early death
– distorted limbs and
– dysfunctional immune systems and organs (including liver and
kidneys) &
– other mishaps
33. Can we clone an individual, Why?
• It might be possible to clone a person’s genes
• But the individual cannot be cloned
• The character, personality, and the features
other than anatomical and physiological that
make up the individual are not precisely
determined by the genotype
34. Dolly… Why not primates?
• The cloning technique used to create Dolly has been
shown not to work in primates
• likelihood is pregnancy losses, abnormal births
• one of the lambs cloned in the same lab soon after
Dolly developed lung problems that caused it to
hyperventilate and regularly pass out
• Recent advances in gene-editing technology, the need
for cloning to correct genetic errors will decline even
further
35. Benefits
• Three main applications for agriculture
– the rapid spread of animals with better genetic
characteristics
– Increased availability of stocks with desirable traints
– Controlled characters
• Theoretically, cloning could also be used to bring
back endangered species
• Somatic cell nuclear transfer may help researchers
better understand early human embryogenesis
and stem cell biology
36. Cloning benefits
• Cloning solve some of the problems that the dairy
industry currently faces in the form of decreased fertility
• Rapidly increase the number, distribution, and availability
of cows and bulls with superior genetics that could allow
increases in milk yield
• Increases in the availability of stock with
– resistance to common diseases such as mastitis, and
– desirable traits associated with milk quality
• The further development of transgenics could
– enhance these functions and also
– increase the ability to produce specialized bioproducts for use
in medicine, pharmaceuticals, and many other industries.
• More difficult to quantify and measure at this early stage of
development
37. Problems associated with cloning
• Large number of technological difficulties and problems to overcome
• Use of cloning technologies are delayed due to;
– current success rates
– variability of results
– costs
– government regulation and
– public perception and acceptance
• In January 2008, the US Food and Drug Administration released a
comprehensive study that concluded that meat and milk from cloned
animals is safe for consumers
• There is still wide-spread uncertainty and significant debate about the
feasibility and acceptability of animal cloning as a technology
• Cloning is commercially available, but the technology still is considered to
be quite inefficient and very costly
38. Extended gestation
• Gestation is usually extended and calves are born much larger
than average
• Due to large offspring syndrome (LOS)
• That leads to dystocia and most animals require cesarean
section
• These large offspring usually have postnatal weakness;
– hypoxia, hypoglycemia, metabolic acidosis, and hypothermia,
all requiring immediate intensive care
• Postnatal problems could be compounded from one
generation to the next
• Cloning will reduce genetic diversity and result in
problems of fertility and disease susceptibility
39. Inbreeding and loss of genetic variation
• Unlimited numbers of identical animals could be produced with
cloning
• Overpopulation of the same genetic makeup could result in inbreeding
and loss of genetic variation, which is not desirable
• With careful management and planning of breeding schemes, these
problems should not occur
• When used correctly, cloning of selected livestock potentially offers
many advantages in animal breeding and production:
– One of which is to preserve biodiversity
• If done without limitations;
– also has the potential to reduce genetic variability
– even in large dairy cattle populations without cloning, a substantial
reduction in genetic variability is already occurring
– because of the massive use of relatively small numbers of sires which are
quite often genetically related
40. Can we overcome?
• New technologies could help to overcome such problems
• Preimplantation genetic diagnosis (PGD)
– reducing the costs of some of the problems associated with
cloning and other advanced breeding technologies
– Embryos can be pre-screened, thus allowing the elimination
of genetically abnormal embryos
– Same technique used to select embryos with economically
beneficial traits
• Clones may be phenotypically similar in simply inherited
characteristics (identical in color, shape, size, etc.)
41. Similarity in cloned individuals
• Gnetic performance may not be exactly the same as the
clonal parents
• Some similarity depending on the heritability of the
characteristics
• In most cases there is no certainty that a clone will be superior,
and in many cases, the clone may actually be inferior
• Cloning could provide faster dissemination of superior genetic
material to the population than previous breeding schemes
have achieved
• but costs are currently extremely high and
• Legal, ethical, and economic questions remain
42. Ethical aspects
• UNESCO's Universal Declaration on the Human Genome and Human
Rights asserts that the reproductive cloning of human beings is
contrary to human dignity
• A potential life represented by the embryo is destroyed when
embryonic cells are used
• The inherent unreliability of cloning technology would be damaging
to cloned individuals
• Non-human animals also possess certain moral rights as living
entities and should therefore be afforded the same ethical
considerations as human beings
• Stand against the exploitation of animals in scientific research on
cloning, cloning for food production, or other uses like therapeutic
purposes etc
43. Different difficulties of human clones
– Human cloning might change the shape of family structure by
complicating the role of parenting within a family of convoluted
kinship relations
• Eg. a female DNA donor would be the clone's genetic twin rather than
mother
– These facts complicate the genetic and social relationships between
mother and child
– As well as the relationships between other family members and the
clone
– Clone would act identically to the human from which they were
cloned: legal, ethical and moral conflicts
– This could infringe on the right to self-determination
44. Cloning: moral issues
• Cloned animals are used in scientific and medical research such
as;
– therapeutic cloning, stem cell research and human antibody production
• It can be painful for the animal and often result in mental and
physical damage
• Clones created for medical purpose have very poor quality of
life as research procedures are constantly being conducted on
them
• Pet cloning: overwhelming numbers of unwanted companion
animals
• Companies that offer pet cloning are deceiving and exploiting
grieving pet owners
Editor's Notes
From a practical point of view then, cloning could be used to increase the number, distribution, and availability of cows and bulls with superior genetics for increased milk yield, increased availability of stock with resistance to common diseases like mastitis, and increased availability of stock with desirable genetic traits associated with milk quality. The further development of transgenics will enhance each of these functions