Cloning

Question 1

Define the term clone

Answer 1

The offspring produced as a results of cloning.

Question 2

Define the term asexual reproduction

Answer 2

The production of genetically identical offspring from a single parent

Question 3

Define the term reproductive cloning

Answer 3

Using artificial cloning methods to produce 2 or more individuals that are clones of each other

Question 4

Define vegetative propagation

Answer 4

The artificial production of natural clones for use in horticulture and agriculture

Question 5

Define perennating organ and describe the link between perennating organs and vegetative propagation

Answer 5

1. Plant structures which allow them to survive adverse conditions. They contain stored food and can remain dormant in the soil
2. They store enough nutrients to sustain the organism during the unfavourable season, and develops into one or more new plants the following year. .
3. Perennation is closely related with vegetative reproduction, as the organisms commonly use the same organs for both survival and reproduction.

Question 6

Describe 4 ways in which plants naturally clone.

Answer 6

Vegetative propagation

1. Bulbs- The leaf base swell with stored food from photosynthesis. Buds form internally which develop into new shoots and new plants in the next growing season
2. Runners- A lateral stem grows away from the parent plant and roots develop where the runner touches the ground. A new plant develops- the runner eventually withers away leaving the new plant independent
3. Rhizomes- A rhizome is a specialised horizontal stem running underground, often swollen with stored food. Buds develop and form new vertical shoots which become individual plants.
4. Stem tubers- The tip of an underground stem becomes swollen with stored food to form a tuber or storage organ. Buds on the storage organ develop to produce new shoots.

Question 7

Define horticulture

Answer 7

The science and art of growing fruits, vegetables, flowers, or ornamental plants.

Question 8

Define agriculture

Answer 8

The science or practice of farming, including cultivation of the soil for the growing of crops and the rearing of animals to provide food, wool, and other products

Question 9

Describe how the production of natural clones is exploited in horticulture.

Answer 9

1. Splitting up bulbs, removing young plants from runners and cutting up rhizomes increase plant numbers cheaply
2. And the new plants have exactly the same genetic characteristics of their parents.

Question 10

Define the term “taking cuttings” and describe how the process is used in horticulture.

Answer 10

1. Short sections of stems are taken and planted either directly into the ground or in pots.
2. Rooting hormone is often applied to the base of a cutting to encourage new growth of new roots
3. Roots grow and the cutting is now a complete plant that is a clone of the parent plant

Question 11

Describe 6 ways in which the success rate of taking cuttings can be increased.

Answer 11

1. Use a non-flowering stem- Resources (e.g. glucose) are not needed to make and sustain the cells of flowers (which don’t photosynthesise and therefore don’t make glucose for themselves) so more can be used to support root growth.
2. Make an oblique cut in the stem- Larger surface area for new roots to grow from. Larger surface area for rooting hormone to adhere to.
3. Use hormone rooting powder- More of the totipotent cells in meristematic regions are triggered to produce roots or it has antifungal properties.
4. Reduce leaves to two or four- Reduces surface area, so reduce transpiration rate. Because the cutting has no roots water uptake is low (very low surface area for water uptake) so water loss must be minimised in order to keep the cutting alive. Some leaves remain for photosynthesis.
5. Keep cutting well watered- Because the cutting has low water uptake water must be in plentiful supply to ensure the cutting gets enough water.
6. Cover the cutting in a plastic bad for a few days- Traps the water lost in transpiration. Air around stomata is humid. Lower water potential gradient from inside the leaf to outside across the stomata. Less water lost by transpiration.

Question 12

Give 5 examples of crops that are propagated by cloning.

Answer 12

Bananas, sugar cane, sweet potatoes, cassava, coffee and tea bushes.

Question 13

Describe the advantages and disadvantages of propagating crops by cloning.

Answer 13

1. Much faster
2. Guarantees quality of plants- genetically identical
3. Lack of genetic variation in the offspring- new disease or pest or climate change may occur

Question 14

Define tissue culture

Answer 14

The method of growing plant cells, in isolation from the parent plant under sterile conditions in or on a nutrient culture medium of known composition

Question 15

Define micropropagation

Answer 15

The process of making very large numbers of genetically identical offspring from a single parent using tissue culture techniques.

Question 16

Define explant

Answer 16

The material removed from a parent plant for tissue culture.

Question 17

Define callus

Answer 17

A mass of undifferentiated plant cells that has been grown from an explant.

Question 18

Describe 5 reasons why micropropagation might be used to clone plants.

Answer 18

It is used to produce plants when a desirable plant
1. Does not readily produce seeds- Sexual reproduction not feasible so micropropagation is an alternative way to reproduce the plant.
2. Doesn’t respond well to natural cloning-
micropropagation is another way to clone plants if natural cloning isn’t feasible.
3. It is very rare- Sexual reproduction may be unlikely if a different individual is needed to pollinate the plant. Micropropagation is the best way to produce a very large number of individuals very quickly.
4. Has been genetically modified or selectively bred with difficulty- One cloning method is required so that offspring are genetically identical to the desired plant.
Micropropagation can produce a very large number of new plants very quickly.
5. Required to be pathogen-free - Only a few cells are used to make each new plant in micropropagation and the method uses aseptic techniques so this minimises the likelihood of new plants carrying pathogens that were in or on the parent plant.

Question 19

Describe the process of micropropagation by callus tissue culture.

Answer 19

1. Take a small sample of tissue from the plant you want to clone- the meristem tissue from shoot tips and axial buds - explants
2. Sterilise the explant in bleach/ ethanol/ sodium dichloroisocyanurate.
3. Place in sterile growth medium, which contain a balance of plant hormones and contain glucose/ amino acids/ nitrates/ phosphates
4. Contain high levels of auxins and cytokines which stimulate mitosis
5. The cells proliferate forming a mass of identical and undifferentiated cells known as a callus.
6. The callus is divided up and individual cells or clumps are transferred to a new culture medium- sub-cultures- aseptic conditions
7. The plant hormone ratio is changed to stimulate the development of tiny genetically identical plantlets.
8. They are transferred to a greenhouse or soil where there are less controlled environment.

Question 20

Give 9 examples of plants that are commonly produced by micropropagation.

Answer 20

Bananas, potatoes, sugar cane, cassava, strawberries, grapes, chrysanthemums, Douglas firs, orchids.

Question 21

Describe the arguments for and against micropropagation.

Answer 21

For
1. Allows for the rapid production of large numbers of plants with know genetic make-up which will yield very good crops.
2. Culturing meristem tissue produces disease-free plants
3. It makes it possible to produce viable numbers of plants after genetic modification
4. It provides a way of producing very large numbers of new plants which are seedless and therefore sterile to meet consumer tastes.
5. It provides a way of growing plants which are naturally relatively infertile or difficult to grow from seeds
6. It provides a way of reliably increasing the numbers of rare or endangered plants.
Against.
1. Produced monoculture- genetically identical- so are all susceptible to the same diseases or changes in growing conditions.
2. Relatively expensive process and requires skilled workers
3. The explants and plantlets are vulnerable to infection by moulds and other diseases through the production process
4. If the source material is infected with a virus all of the clones will also be affected
5. In some cases large numbers of new plants are lost in the production process.

Question 22

Describe 4 examples of natural cloning in animals.

Answer 22

1. Some animals (starfish) can regenerate entire animals from original if damaged
2. Flatworms and sponges fragment and from new identical animals as part of their normal reproductive cycle
3. Hydra produce small buds on the side of their body which develop into genetically identical clones.
4. Monozygotic twins- The early embryo splits to form tow separate embryos

Question 23

Define monozygotic twins

Answer 23

1. Twins formed from a single fertilised egg.

Question 24

State the two ways of artificially cloning animals.

Answer 24

1. Artificial twinning/ splitting embryos

2. Somatic cell nuclear transfer

Question 25

Describe the process of artificial twinning/ splitting embryos

Answer 25

1. The animal with desirable traits is treated with hormones so she super ovulates releasing more mature ova than normal
2. The ova may be fertilised normally or by artificial insemination by a male with particularly good traits. The early embryos are gently flushed out of the uterus.
3. Alternatively the mature eggs are removed and fertilised by the bull semen in the lab
4. Usually before or around day 6, when the cells are still totipotent, the cells of the early embryo are split to produce several smaller embryos each capable of growing on to form a healthy full-term baby animal.
5. Each of the split embryos is grown in the lab for a few days to ensure all is well before it is implanted into a surrogate mother. Each embryo is implanted into a different embryo as single pregnancies carry fewer risks than twin pregnancies
6. The embryos develop into foetuses and are born normally so a number of identical cloned animals are produced by different mothers.

Question 26

Describe the process of cloning animals by nuclear transfer.

Answer 26

1. Egg donor is super ovulated with hormones to produce many eggs, harvested from the ovaries.
2. A donor cell is taken from the adult organism to be cloned. It can be male or female, & allows production of another organism of a species using all possible genetic material, and without needing a breeding female of the species.
3. The nucleus is removed from the mature ovum-enucleated
4. The nucleus is removed from a somatic cell of an adult animal.
5. The nucleus from the adult somatic cell is placed into the enucleated ovum and given a mild electric shock so it fuses and begins to divide rapidly.
6. Surrogate mother has uterus made ready by hormonal treatment: increased vascularisation, & uterus wall prepare for pregnancy.
7. The embryo that develops is transferred into the uterus of a third animal where it develops to term
8. The new animal is a clone of the animal from which the original somatic cell is derived, although the mitochondrial DNA will come from the egg cell.
9. Known as reproductive cloning as live animal is the end result.

Question 27

Describe the arguments for animal cloning.

Answer 27

1. AT- enables high-yielding farm animals to produce many more offspring than normal reproduction
2. AT- enables the success of a sire (male animal) at passing on desirable genes to be determined. If the first cloned embryo results in a successful breeding animal, more identical animals can be reared form the remaining frozen clones.
3. SCNT- enables GM embryos to be replicated and to develop, giving many embryos from one engineering procedure- important in process of pharming.
4. SCNT- enables scientist to clone specific animals e.g. replacing pets or cloning race horses
5. SCNT- potential to enable rare endangered or even extinct animals to be reproduced. In theory the nucleus from a dried or frozen animal tissue could be transferred to the egg of a similar living species and used to produce clones of species that have been dead for a long time.
6. Can make all offspring a certain gender
7. Avoids mating risks

Question 28

Describe the arguments against animal cloning.

Answer 28

1. SCNT- is a very inefficient process- in most animals it takes many eggs to produce a single cloned offspring
2. Many cloned animals fail to develop to term and miscarry or produce malformed offspring
3. Many animals produced by cloning have shortened lifespan
4. SCNT- has been relatively unsuccessful so far in increasing populations of rare organisms or allowing extinct species to be brought back to life.
5. No genetic variability so makes animals more susceptible to environmental factors
6. Very expensive and requires more technology and is more labour intensive