Cloning is a process where genetically identical types of cells, tissues or organism is being produced. There are two types of cloning- Reproductive and therapeutic cloning.

1. Cloning and its types
By,
Ms. Alisha Mahamud Shaikh
• Introduction of cloning
• Therapeutic cloning: Procedure,
benefits and limitations
• Reproductive cloning: Example,
benefits and limitations

2. • The term cloning is used for describing the process where a genetically identical copy of a cell, tissues or an entire
organism is being produced.
• This process happens in nature, when a cell replicates itself asexually without any changes of the genetic set-up.
Bacteria and yeasts do in fact asexually create new individuals which are genetically identical through a process called
binary fission.
• In the case of whole organism cloning of human beings or other mammals, there are two different methods available.
1. when an embryo is split and subsequently resulting in new individuals. This occurs sometimes naturally when twins or
even triplets are born, and is also a process which may be medically designed.
2. By transferring the nucleus of a cell from a donor cell to a recipient cell, a process called cell nuclear transfer (CNT).
The nucleus has been removed from recipient cell and when the new nucleus and the recipient cell fuse the result is a
hybrid where the nuclear DNA is identical to the donor’s. However, a small amount of the recipient’s DNA, so called
mitochondrial DNA, remains.
Introduction of cloning

3. Cell Nuclear Transfer Technology
applied in
Therapeutic cloning Reproductive Cloning
Embryos may be created for the
purpose of conducting research on
abnormalities, diseases and the effects
of drugs
For creating a new individual based
on the DNA of the donor

4. Therapeutic Cloning
• In therapeutic cloning, the nucleus of a cell,
typically a skin cell, is inserted into a fertilized egg
whose nucleus has been removed.
• The nucleated egg begins to divide repeatedly to
form a blastocyst. Then stem cells are extracted
from the blastocyst and use them to grow cells that
are a perfect genetic match for the patient.
• The cells created via therapeutic cloning can then be
transplanted into the patient to treat a disease from
which the patient suffers.

5. Example of therapeutic cloning
• Research led by investigators at Memorial Sloan-Kettering Cancer Center (MSKCC) has shown that
therapeutic cloning, also known as somatic-cell nuclear transfer (SCNT), can be used to treat
Parkinson's disease in mice.
• The scientists used skin cells from the tail of the animal to generate customized or autologous dopamine
neurons--the missing neurons in Parkinson's disease. The mice that received neurons derived from
individually matched stem cell lines exhibited neurological improvement. But when these neurons were
grafted into mice that did not genetically match the transplanted cells, the cells did not survive well and
the mice did not recover.

6. Benefits of therapeutic cloning
• A major benefit of therapeutic cloning is that the cells are pluripotent. Pluripotent Cells can give rise to all cells in the
body with the exception of the embryo. This means that pluripotent cells can potentially treat diseases in any body
organ or tissue by replacing damaged and dysfunctional cells.
• The risk of immunological rejection is reduced because the patient's own genetic material is used. If a cell line were
created with cells from another individual, the patient's body would be more likely to recognize the foreign proteins
and then wage an attack on the transplanted cells. The ultimate consequence would be a rejected stem cell transplant.
• Therapeutic cloning is also important to enhancing our understanding of stem cells and how they and other cells
develop. This understanding can hopefully lead to new treatments or cures for some of the common diseases affecting
people today.
• The procedure can allow to create stem cell therapies that are patient specific and perfectly matched for the patient's
medical condition.

7. Limitations of therapeutic cloning
• Many attempts are often required to create a viable egg. The stability of the egg with the infused somatic nucleus
is poor and it can require hundreds of attempts before success is attained.
• Therapeutic cloning does result in the destruction of an embryo after stem cells are extracted and this destruction
has stirred controversy over the morality of the procedure.
• To this date, no human being has been successfully cloned but the possibility of this occurring is a frightening
one not only for the general public and policy makers, but also for most of the ethical scientific field.

8. Reproductive Cloning
• Reproductive cloning is defined as the deliberate production of genetically identical individuals. Each newly
produced individual is a clone of the original. Monozygotic (identical) twins are natural clones.
• Clones contain identical sets of genetic material in the nucleus. Thus, cells from two clones have the same DNA and
the same genes in their nuclei.
• True clones have identical DNA in both the nuclei and mitochondria, although the term clones is also used to refer
to individuals that have identical nuclear DNA but different mitochondrial DNA.
• Even if clones are genetically identical with one another, they will not be identical in physical or behavioral
characteristics, because DNA is not the only determinant of these characteristics. A pair of clones will experience
different environments and nutritional inputs while in the uterus.
• Cloning of livestock is a means of replicating an existing favorable combination of traits, such as efficient growth
and high milk production, without 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.

10. Cloning by Embryo splitting
Step I : This procedure begins with in vitro fertilization (IVF): the union outside the woman's body of a sperm and an egg
to generate a zygote.
Step II: The zygote (from here onwards also called an embryo) divides into two and then four identical cells. At this stage,
the cells can be separated and allowed to develop into separate but identical blastocysts, which can then be implanted in a
uterus.
• The limited developmental potential of the cells means that the procedure cannot be repeated, so embryo splitting can
yield only two identical mice and probably no more than four identical humans.
• The DNA in embryo splitting is contributed by germ cells from two individuals—the mother who contributed the egg
and the father who contributed the sperm. Thus, the embryos, like those formed naturally or by standard IVF, have two
parents. Their mitochondrial DNA is identical.

11. Benefits of reproductive cloning
• Multiplication of embryos and animals by cloning:
 The potential application of adult cloning ranges from multiplying prize-winning animals to producing a large number
of genetically identical animals for research purposes.
 Dissemination of genetically superior animals would be made easier through the production of several copies of top
breeding animals and the distribution of clones to production farms, particularly where access to artificial
insemination and other assisted reproductive technologies is limited.
• Recovery of endangered animals
• Production of transgenic animals
 Fibroblasts are obtained from fetuses and are used to produce a primary cell line, which, once established and checked
for chromosomal stability, is transfected by common cell transfection techniques. A selection and reporter gene
construct is usually added to the transgene of interest to enable the isolation of suitable cell clones for nuclear transfer,
namely, those clones that integrated the transgene and express the reporter gene correctly

12. Limitations of reproductive cloning
• Pregnancy losses:
 fetal development seems to be arrested at various stages during gestation, leading to abortions at early and late stages of
fetal development.
 Many aspects of embryo and fetal mortality seem to suggest that the placenta does not develop normally, possibly due to
an inappropriate transition from yolk sac to allantoic nutrition. Growth of the allantois is severely retarded, or even
nonexistent, as characterized by lack of, or reduced, vascularization during early gestation, leading to failure of normal
placentome development.
• Neonatal health problems:
 Increased birth weight and high neonatal mortality are common in cloned calves a phenomenon referred
to as "large offspring syndrome," or LOS.
 poor adrenal gland development and function, low fetal cortisol levels.
 Corticosteroid treatment of the recipient before delivery to accelerate maturation of the fetal lungs, together with oxygen
therapy, may increase survival rates.

13. References:
• Grønning, Terje. (2017). Cloning.
• http://www.explorestemcells.co.uk/therapeuticcloning.html
• Smith LC, Bordignon V, Babkine M, Fecteau G, Keefer C. Benefits and problems with cloning animals. Can
Vet J. 2000;41(12):919-924.
• Cloning: Definitions And Applications. Available from: https://www.ncbi.nlm.nih.gov/books/NBK223960/