22 Cloning

Question 1

What is cloning?

Answer 1

The process of producing genetically identical offspring by asexual reproduction or artificially.

Question 2

What is vegetative propagation?

Answer 2

The production of plant clones from non-reproductive tissues e.g roots, leaves and stems.

Question 3

What does natural plant cloning occur in?

Answer 3

1) Bulbs e.g daffodil, onion
2) Runners e.g strawberry
3) Rhizomes e.g marram grass
4) Stem tubers e.g potato

Question 4

How is natural plant cloning exploited in horticulture?

Answer 4

• Cuttings dipped in rooting powder
• Grafting: Joining the shoot of one plant to the growing stem and root of another plant.
• Layering: Bending a stem of a growing plant downwards so it enters the soil and grows into a new plant.

Question 5

What is micropropagation?

Answer 5

Micropropagation is the process of making large numbers of genetically identical offspring from a same single parent plant using tissue culture techniques.

Question 6

When is micropropagation used?

Answer 6

It is used to produce plants when a desirable plant:

• Has been genetically modified
• Doesn’t readily produce seeds
• Is very rare
• Doesn’t respond well to natural cloning.

Question 7

What are the arguments FOR micropropagation?

Answer 7

• Allows for rapid production of large numbers of plants with known genetic makeup so yields good crops.
• Culturing meristem tissue produces disease-free plants.
• Enables large numbers of seedless plants to be grown and so meets consumer tastes.
• Provides a way to reliably increase numbers of rare/endangered plants.

Question 8

What are arguments AGAINST micropropagation?

Answer 8

• Produces a monoculture: because they’re genetically identical they’re all susceptible to the same diseases
• Relatively expensive and requires skilled workers
• Explants and plantlets are vulnerable to infection by moulds during production process.
• If source material is infected with virus, all clones will be infected.

Question 9

What is artificial twinning?

Answer 9

The process of producing monozygotic twins artificially.

- calves are clones of each other not parents

Question 10

What are the stages in artificial twinning?

Answer 10

1) A cow with desirable traits is treated with hormones so she releases more mature ova than normal.
2) The ova may be fertilised naturally, or fertilised artificially in a lab.
3) When the cells are still totipotent, the cells are split to produce smaller embryos.
4) Each of the split embryos are grown in the lab before implanted into a surrogate mother. (Each embryo implanted into different mother as single pregnancies)

Question 11

What is somatic cell nuclear transfer?

Answer 11

A method of producing a clone from an adult animal by transferring the nucleus from an adult cell to an enucleated egg cell.

Question 12

What are the steps in somatic cell nuclear transfer?

Answer 12

1) The nucleus is removed from a somatic cell of an adult animal.
2) The nucleus is removed from a mature ovum harvested from a different female animal of same species. (It is enucleated)
3) 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.
4) The embryo that develops is transferred into the uterus of a third animal where it develops.

Question 13

What can SCNT be used for?

Answer 13

• Used in pharming: the production of animals that have been genetically engineered to produce therapeutic human proteins in their milk.
• Used to produce genetically modified animals which grow organs and have potential to be used in human transplants.

Question 14

What are the arguments FOR animal cloning?

Answer 14

• Enables high-yielding farm animals to produce more offspring than normal reproduction.
• Enables GM embryos to be replicated and develop, important process in pharming
• Specific animals e.g pets can be cloned
• Has potential to enable rare, endangered species to be reproduced.

Question 15

What are the arguments AGAINST animal cloning?

Answer 15

• Very inefficient process: Takes many eggs to produce single cloned offspring
• Many cloned embryos fail to develop&miscarry or produce malformed offspring.
• Many animals produced by cloning have shortened lifespans.

Question 16

ways of artificially cloning plants :

Answer 16

1) taking cuttings -
- one cutting produces one plant

2) tissue culture/micropropagation -
- makes many clones of plant from one cutting

Question 17

steps of tissue culture

Answer 17

1) Take a small sample of tissue from the plant selected for cloning. Meristem tissue from the shoot tips and axial buds is dissected.
2) The sample is sterilised to kill any microorganisms that would compete for nutrients with the plant cells.
3) The explant is placed in a sterile culture medium containing plant hormones (auxins&cytokinins) which stimulate mitosis. The cells profilerate, forming a mass of identical cells known as a callus.
4) The callus is divided up into individual cells that develop into plantlets and then plants.

Question 18

how to take cuttings ?

Answer 18

• cut plant between nodes at 45 degree angle use scalpel
• dip in rooting powder (typically auxin)
• place in moist soil, cover so there is humid air - reduces transpiration stress
• wait till roots develop