What Is Cloning?

A clone is a cell or organism that is genetically identical, or nearly genetically identical, to another cell or organism from which it originated.

Cloning is the process of producing genetically identical copies of:

• DNA
• cells
• tissues
• organisms

Cloning can occur:

naturally

or it can be performed artificially using:

biotechnology.

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Genetic Information and Cloning

Most of the genetic information needed to produce an organism is contained in its:

DNA.

DNA is organized into:

chromosomes.

When an organism is cloned, the new organism receives essentially the same nuclear genetic information as the organism from which that DNA originated.

Therefore:

same nuclear DNA → very similar genetic information → clone

However, genetically identical does not necessarily mean:

completely identical in appearance or behaviour.

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Genotype vs Phenotype

This distinction is important.

Genotype refers to an organism's genetic makeup.

Phenotype refers to its observable characteristics.

Phenotype is influenced by:

genotype + environment + development.

Therefore, two clones can have essentially the same genotype but develop somewhat different:

phenotypes.

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Natural Cloning

Cloning is not simply a laboratory technology.

It occurs naturally in many:

organisms.

Natural cloning often occurs through:

asexual reproduction.

Only one parent is required, and offspring are produced without the fusion of:

gametes.

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Binary Fission

Many bacteria reproduce through:

binary fission.

During binary fission:

1. The bacterial DNA is copied.

2. The cell grows.

3. The DNA copies separate.

4. The cell divides into two cells.

The resulting cells are generally genetically very similar to the original cell, apart from mutations that may:

occur.

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Vegetative Reproduction in Plants

Plants can naturally produce genetically identical offspring using structures such as:

• runners
• bulbs
• tubers
• rhizomes

This is called:

vegetative reproduction.

The new plants develop from tissues of the parent rather than from seeds produced through sexual reproduction.

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Strawberry Runners

Strawberry plants can produce horizontal stems called:

runners.

A runner grows away from the parent plant.

Where it contacts suitable soil, a new plant can develop.

Because the new plant developed asexually from the parent, it is genetically very similar to the:

parent plant.

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Potato Tubers

Potatoes can reproduce vegetatively using:

tubers.

The "eyes" of a potato contain buds that can develop into new:

shoots.

If a potato tuber is planted, new plants can grow from these buds.

These plants are clones of the plant that produced the:

tuber, aside from mutations.

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Identical Twins

Identical twins are another example of naturally occurring cloning-like development in humans.

They form when one fertilized egg:

splits into two embryos.

Because both embryos developed from the same original zygote, they begin with essentially the same nuclear:

DNA.

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Identical vs Fraternal Twins

Identical twins and fraternal twins form differently.

Identical twins

One egg + one sperm → one zygote → embryo separates

They begin with essentially the same nuclear genetic information.

Fraternal twins

Two eggs + two sperm → two different zygotes

Fraternal twins are genetically similar in the same general way as other biological siblings.

They are not:

clones.

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Artificial Cloning

Humans can also deliberately produce genetic copies using:

artificial cloning techniques.

Artificial cloning can involve:

• cloning plants
• cloning cells
• cloning DNA
• cloning whole organisms

Different techniques are used depending on what scientists want to:

copy.

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Cloning Plants from Cuttings

One of the simplest forms of artificial cloning is taking a:

plant cutting.

A piece of stem is removed from a parent plant.

Under suitable conditions, the cutting can develop:

roots.

It can then grow into a new plant.

The new plant is genetically very similar to the parent because it was produced from the parent's:

cells.

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Why Clone Plants?

Suppose a farmer has a plant with valuable characteristics such as:

• large fruit
• high yield
• desirable flavour
• attractive flowers
• disease resistance

Sexual reproduction mixes genetic information and may produce offspring with different combinations of:

alleles.

Cloning allows the farmer to preserve a successful:

genotype.

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Tissue Culture

Large numbers of plant clones can also be produced using:

tissue culture.

Tissue culture involves growing small pieces of plant tissue under controlled, sterile:

conditions.

The cells can divide and eventually develop into new:

plants.

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Basic Plant Tissue Culture

A simplified process is:

1. Select a plant with desirable characteristics.

2. Remove a small piece of tissue.

3. Sterilize the material and equipment.

4. Place the tissue on a nutrient growth medium.

5. Use suitable plant growth regulators.

6. Allow cells to divide.

7. Encourage shoots and roots to develop.

8. Transfer the young plants to suitable growing conditions.

Many genetically similar plants can be produced from a small amount of original:

tissue.

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Micropropagation

Producing large numbers of plants through tissue culture is often called:

micropropagation.

Micropropagation can produce many plants relatively:

quickly.

It is particularly useful for commercially valuable plants.

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Advantages of Plant Cloning

Plant cloning can:

• produce many plants quickly
• preserve desirable characteristics
• produce genetically uniform crops
• reproduce plants that are difficult to grow from seed
• help propagate rare plants
• produce disease-free planting material when suitable techniques are used

These advantages make cloning important in:

agriculture and horticulture.

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Disadvantage of Genetic Uniformity

Genetic uniformity can also create a:

risk.

Imagine thousands of genetically similar crop plants.

If all are susceptible to the same:

disease,

a disease outbreak could affect a large proportion of the crop.

Sexual reproduction produces more genetic variation, increasing the chance that some individuals may possess:

resistance.

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Genetic Diversity

Genetic diversity refers to genetic differences within a:

population.

Sexual reproduction generally increases genetic variation through:

• meiosis
• crossing over
• independent assortment
• random fertilization

Cloning does not produce these same sources of genetic recombination.

Therefore, extensive cloning can reduce genetic diversity within a cultivated:

population.

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Cloning Animals

Producing a clone of an entire animal is considerably more complicated than taking a plant:

cutting.

One important technique is:

somatic cell nuclear transfer, or SCNT.

SCNT was famously used to produce:

Dolly the sheep.

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Somatic Cell Nuclear Transfer

A somatic cell is an ordinary body cell rather than a:

gamete.

In somatic cell nuclear transfer, the nucleus of a somatic cell is transferred into an egg cell whose own nucleus has been:

removed.

The reconstructed cell can then be stimulated to begin dividing.

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The Basic Steps of SCNT

A simplified SCNT procedure involves:

1. Obtain a somatic cell from the animal to be cloned.

2. Remove the nucleus from an egg cell.

3. Transfer the somatic-cell nucleus into the enucleated egg.

4. Stimulate the reconstructed cell to divide.

5. Allow an early embryo to develop.

6. Transfer the embryo into a surrogate mother.

7. If development is successful, an offspring may be born.

The offspring has nuclear DNA essentially matching the:

nucleus donor.

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Three Animals Can Be Involved

SCNT can involve genetic and biological contributions from three:

animals.

Nucleus donor

Provides the:

nuclear DNA.

Egg donor

Provides the egg cell and its cytoplasm, including:

mitochondria.

Surrogate

Provides the uterus in which the embryo:

develops.

This distinction is important when analyzing cloning.

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Which Animal Is the Clone Of?

Suppose:

Animal A provides the somatic-cell nucleus.

Animal B provides the egg.

Animal C acts as the surrogate.

The offspring's nuclear DNA most closely matches:

Animal A.

Therefore, Animal A is the organism normally described as having been:

cloned.

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Mitochondrial DNA

SCNT introduces an important complication.

Most DNA is found in the:

nucleus.

However, mitochondria also contain a small amount of:

DNA.

The mitochondria in the reconstructed egg generally come from the:

egg donor.

Therefore, an SCNT clone is not necessarily genetically identical in every piece of DNA to the nucleus donor.

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Dolly the Sheep

In 1996, scientists produced a sheep named:

Dolly.

Dolly became famous because she was the first mammal cloned from the nucleus of an adult somatic cell to survive to adulthood.

Her birth demonstrated that genetic information in a differentiated adult cell nucleus could be reprogrammed to direct the development of an entire:

organism.

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Why Was Dolly Important?

Adult cells become:

specialized.

For example:

• muscle cells perform muscle functions
• nerve cells transmit signals
• skin cells form protective tissues

Yet most somatic cells retain essentially the same complete set of nuclear genetic:

information.

Dolly demonstrated that the nucleus from a specialized adult cell could be reprogrammed during cloning.

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Cloning Does Not Copy Age

A clone is not born as an adult copy of another:

organism.

If an adult animal is cloned, the clone begins life as:

an embryo.

It then develops through normal developmental stages.

Therefore, cloning copies genetic information, not the donor's memories, experiences, body size, or:

age.

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Clones Are Not Photocopies

Imagine two cloned animals with essentially the same nuclear:

DNA.

One receives excellent nutrition.

The other experiences poor nutrition.

One develops in a warmer environment.

The other develops in a colder environment.

Their phenotypes may become somewhat:

different.

Genes influence characteristics, but environment and development also matter.

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Cloning and Epigenetics

Cells contain chemical modifications that influence how genes are:

expressed.

These are part of:

epigenetic regulation.

During animal cloning, the transferred nucleus must be reprogrammed so that it can direct embryonic development.

Incomplete or abnormal reprogramming can contribute to developmental:

problems.

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Success Rates

Animal reproductive cloning has historically had relatively low:

efficiency.

Many reconstructed embryos do not develop successfully.

Some pregnancies fail.

Some cloned animals can experience developmental or health:

problems.

This is an important limitation when evaluating animal cloning.

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Reproductive Cloning

Reproductive cloning aims to produce a new whole:

organism.

SCNT followed by embryo transfer into a surrogate is an example.

The goal is for the embryo to develop through pregnancy and eventually produce a living:

offspring.

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Therapeutic Cloning

The term therapeutic cloning generally refers to using cloning techniques such as SCNT to produce cells for research or potentially:

medicine,

rather than producing a cloned individual.

The goal is to obtain cells that may be useful for studying:

• development
• disease
• cell differentiation
• regenerative medicine

This is different from reproductive cloning.

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Stem Cells

A stem cell is a cell capable of dividing and producing other types of:

cells.

Some stem cells can develop into several specialized cell types.

Researchers study stem cells because they may help us understand:

• development
• tissue repair
• disease
• cell specialization

Cloning technologies and stem-cell research can therefore overlap in some areas of biotechnology.

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DNA Cloning

Scientists can also clone pieces of:

DNA.

For example, a gene can be inserted into a bacterial:

plasmid.

The plasmid is introduced into bacteria.

As the bacteria reproduce, they also copy the:

plasmid DNA.

This can produce many copies of the inserted gene.

This process is known as:

molecular cloning or DNA cloning.

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Cell Cloning

Scientists can also produce populations of cells derived from a single original:

cell.

These cells can be useful for:

• biological research
• studying mutations
• testing treatments
• producing biological products

Therefore, the word cloning does not always mean producing an entire animal.

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Types of Cloning

We can divide cloning into several broad categories:

Natural cloning

Occurs without deliberate human intervention.

Examples:

binary fission, vegetative reproduction, identical twins

Artificial plant cloning

Examples:

cuttings and tissue culture

Reproductive cloning

Produces a whole cloned organism.

Therapeutic cloning

Produces cells for research or potential medical applications.

Molecular cloning

Produces copies of selected DNA sequences.

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Potential Benefits of Cloning

Cloning technologies can have several possible:

benefits.

These depend strongly on the type and purpose of cloning.

Potential applications include:

• agriculture
• conservation
• medicine
• scientific research
• horticulture
• biotechnology

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Benefit: Agriculture

Cloning can reproduce organisms with valuable:

characteristics.

For plants, these might include:

• high yield
• large fruit
• desirable flavour
• disease resistance
• attractive flowers

Cloning allows these characteristics to be preserved rather than reshuffled through sexual:

reproduction.

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Benefit: Rapid Plant Production

Tissue culture can produce very large numbers of plants from a relatively small amount of:

starting material.

This can be useful when growers need many genetically similar plants:

quickly.

Commercial plant production therefore makes extensive use of:

micropropagation.

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Benefit: Conservation

Cloning technologies have sometimes been investigated as tools for conserving:

endangered species.

Cells preserved from an animal could potentially provide genetic material for reproductive:

technologies.

However, cloning alone cannot solve the major causes of extinction such as:

• habitat destruction
• climate change
• poaching
• pollution
• low genetic diversity

Conservation requires protecting viable populations and their:

habitats.

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Benefit: Scientific Research

Cloned cells and genetically similar organisms can be valuable in:

experiments.

If organisms have similar genetic backgrounds, researchers can better investigate the effects of:

• environment
• treatments
• diet
• disease
• particular genetic changes

Reducing genetic variation can help researchers control an experimental:

variable.

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Benefit: Medical Research

Cloning techniques can help scientists investigate:

• early development
• gene regulation
• stem cells
• disease mechanisms
• cell differentiation

These studies can improve our understanding of:

human biology.

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Potential Problems With Cloning

Cloning also presents important biological and practical:

limitations.

These include:

• low success rates in animal cloning
• developmental abnormalities
• possible health problems
• reduced genetic diversity
• high cost
• technical difficulty
• animal welfare concerns

These factors must be considered alongside potential benefits.

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Cloning and Genetic Diversity

Imagine a crop population consisting almost entirely of one:

clone.

If a pathogen can infect that genotype, many plants may be:

susceptible.

A genetically diverse population may contain individuals with different levels of resistance.

Therefore:

genetic uniformity can increase vulnerability to environmental change or disease.

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Cloning and Evolution

Evolution depends on:

heritable variation.

Cloning produces little new genetic variation by itself, although mutations can still occur.

If a population relies heavily on cloning, genetic diversity may be lower than in a sexually reproducing:

population.

This can reduce the range of genetic variation available for natural selection.

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Animal Welfare Concerns

Animal cloning can involve:

• unsuccessful embryo development
• failed pregnancies
• repeated procedures
• health complications
• surrogate animals

This raises important questions about:

animal welfare.

When evaluating cloning, scientists and society must consider not only successful cloned animals but also unsuccessful attempts.

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Ethical Concerns

Ethics involves questions about what people:

should do,

not simply what technology makes possible.

Questions surrounding cloning can include:

• Is it acceptable to clone animals for human purposes?
• How much animal suffering is acceptable in research?
• Should endangered species be cloned?
• Should human reproductive cloning ever be permitted?
• Who would control access to cloning technologies?
• How should cloned embryos be treated in research?

These questions involve science, ethics, law, culture, and personal values.

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Human Reproductive Cloning

Human reproductive cloning would aim to produce a child genetically very similar to a nuclear DNA:

donor.

It raises major concerns involving:

• safety
• medical risk
• identity
• consent
• family relationships
• exploitation
• rights and welfare

Human reproductive cloning has not become an accepted clinical reproductive practice.

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Cloning Would Not Copy a Person's Mind

Even if two people had extremely similar genomes, they would not necessarily have identical:

personalities.

A person's development is influenced by:

• experiences
• family
• culture
• education
• environment
• chance events during development
• gene expression

Cloning DNA does not clone:

memories, experiences, or identity.

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Clone vs Genetic Engineering

These concepts are often confused.

Cloning

produces genetic copies.

Genetic engineering

deliberately changes genetic material.

An organism can be cloned without having its DNA deliberately modified.

An organism can also be genetically engineered without being:

cloned.

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Cloning vs Sexual Reproduction

Cloning

Usually involves one genetic source for the nuclear genome.

Produces offspring genetically very similar to that source.

Creates relatively little genetic variation.

Sexual reproduction

Combines genetic information from two gametes.

Produces genetically varied offspring.

Creates new combinations of:

alleles.

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Cloning vs Asexual Reproduction

Asexual reproduction naturally produces:

clones or near-clones.

Cloning is therefore not fundamentally unnatural as a biological:

process.

Artificial cloning uses human-controlled methods to reproduce DNA, cells, tissues, or organisms.

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Worked Example 1

A gardener cuts a stem from a plant and encourages it to grow roots.

What has occurred?

Artificial vegetative propagation.

The new plant is a:

clone of the parent plant, aside from any mutations.

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Worked Example 2

A strawberry plant produces a runner that develops into another plant.

Natural or artificial cloning?

Natural cloning through vegetative reproduction.

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Worked Example 3

A nucleus is removed from a sheep's body cell and transferred into an egg whose nucleus has been removed.

What technique is being used?

Somatic cell nuclear transfer (SCNT).

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Worked Example 4

Animal A provides the nucleus.

Animal B provides the egg.

Animal C carries the pregnancy.

Which animal provides most of the clone's genetic information?

Animal A.

The nuclear DNA comes from the:

nucleus donor.

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Worked Example 5

Two cloned plants grow to different heights.

Does this prove they have different genotypes?

No.

Different environmental conditions can produce different:

phenotypes even when the plants have essentially the same genotype.

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Worked Example 6

A farmer wants 10,000 plants with the same desirable fruit characteristics.

Why might tissue culture be useful?

It can:

rapidly produce many genetically similar plants from selected tissue.

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Worked Example 7

A disease kills nearly every plant in a field of genetically identical clones.

What disadvantage of cloning does this illustrate?

Low genetic diversity can make a population vulnerable to the same disease.

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Common Mistake: A Clone Is an Exact Copy in Every Way

A clone may have nearly identical genetic information but may not have an identical:

phenotype.

Environmental conditions and developmental processes can create differences.

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Common Mistake: Cloning Creates an Adult Copy

A cloned animal begins development as:

an embryo.

It must grow and develop like other organisms.

Cloning does not instantly create an adult copy.

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Common Mistake: Clones Have the Same Memories

Memories are not copied simply by copying:

DNA.

A cloned organism develops its own nervous system and has its own experiences.

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Common Mistake: All Cloning Happens in Laboratories

Cloning occurs naturally.

Examples include:

• bacterial binary fission
• plant vegetative reproduction
• identical twins

Artificial cloning is only one type of cloning.

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Common Mistake: Cloning and Genetic Engineering Are the Same

Cloning means:

making genetic copies.

Genetic engineering means:

modifying genetic material.

They are different biotechnology techniques.

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Common Mistake: Cloning Produces Zero Genetic Differences

Mutations can occur during cell division.

SCNT clones may also differ in mitochondrial DNA from the nuclear donor.

Epigenetic differences can also affect gene:

expression.

Therefore, "genetically identical" is often a useful simplification rather than absolute identity at every molecular level.

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Evaluating Cloning

A good scientific evaluation should consider both:

benefits and concerns.

For example:

Possible benefit

Cloning can rapidly reproduce a valuable crop variety.

Possible concern

The resulting population may have low genetic diversity.

Possible benefit

Cloning technologies can support biological research.

Possible concern

Animal cloning can involve failed embryos and welfare problems.

A strong evaluation considers:

evidence, purpose, benefits, risks, alternatives, and ethical implications.

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Check Your Understanding

1. Define cloning.

2. What is a clone?

3. Why are clones genetically similar?

4. Explain why clones may not have identical phenotypes.

5. Give three examples of natural cloning.

6. Explain how binary fission produces clones.

7. What is vegetative reproduction?

8. Explain how strawberry runners produce clones.

9. Explain how potato tubers can produce clones.

10. Why can identical twins be considered natural clones?

11. Explain how identical and fraternal twins differ.

12. Describe how a plant can be cloned using a cutting.

13. What is tissue culture?

14. What is micropropagation?

15. Give three benefits of plant cloning.

16. Why might farmers clone plants with desirable characteristics?

17. What is one disadvantage of producing a genetically uniform crop?

18. Why is genetic diversity important?

19. What does SCNT stand for?

20. What is a somatic cell?

21. Describe the main stages of SCNT.

22. What happens to the nucleus of the egg during SCNT?

23. Where does the transferred nucleus come from?

24. What is the role of the surrogate animal?

25. Which animal contributes most of the clone's DNA?

26. Why might an SCNT clone have different mitochondrial DNA from its nucleus donor?

27. Why was Dolly the sheep scientifically important?

28. Why doesn't cloning produce an adult organism immediately?

29. Why can cloned animals develop differently?

30. What is reproductive cloning?

31. What is therapeutic cloning?

32. Explain one way cloning technologies could contribute to medical research.

33. What is molecular cloning?

34. Explain one possible agricultural benefit of cloning.

35. Explain one possible conservation application.

36. Why can't cloning alone solve the extinction crisis?

37. Give two animal welfare concerns associated with cloning.

38. Explain one ethical concern associated with human reproductive cloning.

39. Explain the difference between cloning and genetic engineering.

40. Evaluate the statement: "Because cloning can produce useful organisms, it has no disadvantages."

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Key Terms

• Clone: Cell or organism genetically identical or nearly genetically identical to another from which it originated.
• Cloning: Production of genetically identical or nearly identical copies of DNA, cells, tissues, or organisms.
• Asexual reproduction: Reproduction involving one parent without fusion of gametes.
• Vegetative reproduction: Asexual reproduction in plants using non-reproductive structures such as runners, tubers, or bulbs.
• Binary fission: Asexual process in which one cell divides into two.
• Plant cutting: Piece of a plant used to produce a genetically similar new plant.
• Tissue culture: Growth of cells or tissues under controlled conditions.
• Micropropagation: Production of many plant clones using tissue culture.
• Somatic cell: Body cell that is not a gamete.
• SCNT: Somatic cell nuclear transfer; cloning technique involving transfer of a somatic-cell nucleus into an enucleated egg.
• Enucleated egg: Egg cell whose nucleus has been removed.
• Nucleus donor: Organism providing the nucleus used during SCNT.
• Surrogate: Individual that carries a developing embryo.
• Reproductive cloning: Cloning intended to produce a whole organism.
• Therapeutic cloning: Use of cloning techniques to produce cells for research or potential medical applications.
• Molecular cloning: Production of copies of DNA sequences.
• Stem cell: Cell capable of dividing and developing into other cell types.
• Genetic diversity: Genetic variation among individuals in a population.
• Phenotype: Observable characteristics of an organism.
• Epigenetics: Changes in gene regulation that do not require changes to the underlying DNA sequence.

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Key Takeaways

• Cloning produces genetically identical or nearly genetically identical copies.
• DNA, cells, tissues, plants, and whole organisms can be cloned.
• Cloning occurs both naturally and artificially.
• Asexual reproduction commonly produces natural clones.
• Bacterial binary fission produces genetically similar daughter cells.
• Strawberry runners and potato tubers are examples of natural vegetative reproduction.
• Identical twins begin with essentially the same nuclear DNA.
• Plant cuttings can be used to produce artificial clones.
• Tissue culture can produce large numbers of genetically similar plants.
• Micropropagation is widely used in horticulture and agriculture.
• Cloning allows desirable plant characteristics to be preserved.
• Genetic uniformity can also make populations vulnerable to the same diseases or environmental changes.
• Animal cloning can be performed using somatic cell nuclear transfer (SCNT).
• SCNT transfers the nucleus of a somatic cell into an egg whose nucleus has been removed.
• The clone's nuclear DNA comes primarily from the nucleus donor.
• Mitochondrial DNA generally comes from the egg donor.
• A surrogate provides the environment in which the cloned embryo develops.
• Dolly the sheep demonstrated that an adult somatic-cell nucleus could be reprogrammed to support development of a whole organism.
• A cloned animal begins as an embryo rather than appearing as an adult copy.
• Clones can have different phenotypes because environment and development also affect characteristics.
• Cloning does not copy memories, experiences, personality, or identity.
• Reproductive cloning aims to produce a whole organism.
• Therapeutic cloning focuses on cells for research or potential medical use.
• Molecular cloning produces copies of DNA.
• Cloning can benefit agriculture, horticulture, research, and potentially conservation and medicine.
• Animal cloning can have low efficiency and raise animal-welfare concerns.
• Extensive cloning can reduce genetic diversity.
• Cloning endangered organisms cannot replace habitat protection and population conservation.
• Human reproductive cloning raises major safety and ethical concerns.
• Cloning and genetic engineering are different: cloning copies genetic material, while genetic engineering deliberately modifies it.
• Evaluating cloning requires considering its purpose, evidence, benefits, biological limitations, risks, alternatives, and ethical implications.