Cloning

Question 1

What is cloning?

Answer 1

Process of creating cells or organisms that are genetically identical to the parent organism from the cells of the parent.

Question 2

What are the different ways in which clones are produced.

Answer 2

• Asexual reproduction.
• Artificial cloning by nuclear transfer.
• Artificial cloning by tissue culture.
• Artificial vegetative propagation.

Question 3

What are the advantages of asexual reproduction?

Answer 3

• Quick, allowing organisms to reproduce rapidly and take competitive advantage over resources in habitat.
• Can be carried out if sexual reproduction not possible/fails (no second parent).
• Offspring genetically identical to parent, so will possess all characteristics that allow parent to be well adapted to environment.

Question 4

What are the disadvantages of asexual reproduction?

Answer 4

• Does not produce genetic variation, so all offspring susceptible to and will be affected by same weaknesses. E.g. A new disease or an unsuitable change in climate could wipe out whole offspring population.
• Offsprings are generally in vicinity of parent, so there will be competition.

Question 5

What is vegetative propagation?

Answer 5

Production of structures from non-reproductive tissue of parent plant that develop into completely new individuals, often genetically identical to parent, so are considered clones.

Question 6

How does vegetative propagation occur in elm trees?

Answer 6

1. Suckers grow from sucker buds scattered across root that are normally dormant,
2. Sucker buds activated and suckers begin to grow from shallow roots when elm tree experiences stress (e.g. Disease, damage) or is dying.
3. Suckers are usually well spaced out from parent to avoid factor/s causing stress on parents but all grow in a circle around parent called clonal patch.
4. They eventually grow into completely new elm trees that are clones of the parent.

Question 7

How are plants cloned artificially?

Answer 7

• Stem cuttings.
• Leaf cuttings.
• Root cuttings.
• Grafting.
• Tissue cultures.

Question 8

How are stem cuttings carried out?

Answer 8

• Part of a plant stem is cut from parent plant.
• The stem section is replanted in soil and treated with plant hormones to encourage root growth.
• Stem grows into full plant and is clone of parent.

Question 9

How are graftings carried out?

Answer 9

• Grafting can only be used for cloning woody plants.
• A shoot section (scion) of one plant is joined to the rootstock of another plant and is held in place.
• The scion grows into new plant and eventually fuses with rootstock.

Question 9

How are tissue cultures carried out?

Answer 9

1. Tissue sample (called explant) containing many meristematic cells are taken (usually shoot tip).
2. Cells are sterilised to kill potential contaminants.
3. Cells are placed on nutrient growth medium and allowed to divide into unspecialised mass called callus.
4. Single callus cells are then taken and placed into growth medium containing shoot stimulating hormones.
5. Shoots are then transferred to medium containing root stimulating hormones.
6. Developing plantlets are then transferred into compost and left to grow in greenhouse (or other protected environments).

Question 10

What are the advantages of tissue cultures over traditional plant cloning techniques?

Answer 10

• Some plants to not reproduce well from cuttings/ graftings.
• Large number of cloned offsprings can be produced quicker compared to traditional techniques.
• Minimal damage to parent plant as only small tissue sample needed as opposed to say, a whole stem.
• Cloned plants can be produced at any time of the year as tissue cultures are carried out indoors.

Question 11

What are the advantages of plant cloning?

Answer 11

• Parent’s desirable characteristics are always passed to offspring, due to having same genetic information.
• Cloned plants can be produced at any time of the year as tissue cultures are carried out indoors.
• Sterile plants are allowed to reproduce.
• Quick as some plants take long time to grow from seeds.
• Clones grow at same rate so are ready to harvest around same time, reducing farmers’ costs.

Question 12

What are the disadvantages of cloning plants?

Answer 12

• Parent’s undesirable characteristics are also always passed on.
• No genetic variation, so any weakness parent has is possessed by whole cloned population. E.g. Disease, climate change.
• Production costs very high (especially tissue cultures) due to expensive equipment, extensive energy consumption and training workers.

Question 13

What are the methods for cloning animals?

Answer 13

• Embryo splitting.

- Nuclear transfer.

Question 14

How is embryo splitting carried out?

Answer 14

1. Early developing embryo (8-16 cells) taken from womb of mother and put into cell culture.
2. Embryo carefully split into multiple embryos and are transferred to womb of genetically unrelated surrogate mothers.
3. Embryos develops in womb of surrogates to produce identical offsprings.

Question 15

How is nuclear transfer carried out (in sheep)?

Answer 15

1. Somatic (body) cell from sheep A taken and nucleus extracted.
2. Egg cell from sheep B is enucleated.
3. Sheep A nucleus inserted into the enucleated sheep B egg cell.
4. Egg cell stimulated to divide into embryo in vitro.
5. Developing embryo then implanted into another sheep, acting as surrogate mother.
6. Lamb produced is genetically identical to sheep A so is clone.

Question 16

What are the advantages of cloning animals?

Answer 16

• Parent’s desirable characteristics are always passed to offsprings due to having same genetic information.
• Infertile animals can reproduce and pass on good traits.
• Large number of offsprings can be produced very quickly.
• Can be used to clone rare species and preserve population when suitable mates are difficult to find.

Question 17

What are the disadvantages of cloning animals?

Answer 17

• Parent’s undesirable characteristics are always passed to offsprings, so they are vulnerable to same weaknesses.
• Technically very complex and requires many failed attempts to produce success, which may be costly and time consuming.
• Cloned offsprings may not live as long as natural offspings.

Question 18

What is reproductive cloning?

Answer 18

Creation of whole genetically identical organism (clone) using cells from the parent.

Question 19

What are the uses of reproductive cloning?

Answer 19

• Used for testing drugs and other research. Individuals are genetically identical, eliminating any variations caused by genetic differences, making results more reliable.
• Used in agriculture to replicate individuals with desirable characteristics.
• Used to clone endangered species and increase population size in endangered species if mates are difficult to find/ sexual reproduction slow.

Question 20

What is non-reproductive cloning?

Answer 20

Use of cells in parent to produce embryonic stem cells with identical genetic information to parent. This is also called therapeutic cloning.

Question 21

What are the uses of non-reproductive cloning?

Answer 21

• Produces embryonic stem cells of a (developed) individual.
• These are totipotent, so can differentiate into any type of tissue cell.
• They can be used to grow replacement tissue for those damage due to disease/ accident. E.g. Replace nervous tissue lost to MS, replace cardiac tissue lost after heart attack etc.
• Can be used to potentially grow replacement organs.
• These stem cells are genetically identical to parent cells, so won’t be classed as foreign by immune system, so no rejection suffered.

Question 22

What are the ethical issues concerned with human cloning?

Answer 22

• Use of embryos as source of stem cells destroys embryo, which had the potential of developing into human being.
• Cloned humans, if produced, may have reduced quality of lived as consequence of social acceptance and identity.
• Cloning may undermine the traditional ‘family’.