Chapter 22 Cloning and Biotechnology

What is cloning?

• The production of identical copies of organisms, cells or DNA.

What is a clone?

• Genetically identical organism or group of genetically identical cells derived from a single parent.

What is vegetative propagation?

• A form of asexual reproduction where new, genetically identical plants are formed from a structure that develops from the parent plant.

• The new plant is propagated from the parent.

What are some examples of propagation in plants?

• Bulbs in daffodils- buds form internally which develop into new shoots and new plants.

• Runners in strawberry plants- lateral stem grows away from the parent plant.

• Rhizomes in marram grass- horizontal stem that runs underground, buds develop and form new shoots.

• Stem tubers in potatoes- buds on storage organs develop to produce new shoots.

How are natural clones used in horticulture?

• Exploited by farmers and gardeners to produce new plants by splitting up bulbs and cutting runners from plants, this allows them to increase plant numbers cheaply.

• All the new plants have exactly the same genetic characteristics as the parent.

• Can also use propagation from cuttings to reduce the time from planting to cropping and to ensure the quality of the plants.

What is micropropagation?

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

When is micropropagation used?

• When a desired plant doesn’t:

  • Readily produce seeds

  • Doesn’t respond well to natural cloning

  • Is very rare

  • Is required to be ‘pathogen-free’ by growers- like bananas and strawberries

What are the steps of micropropagation?

1. Take a small sample of tissue from the plant you are wanting to clone- this sample is usually taken from the meristem tissue of the root tips and this is dissected in sterile conditions to prevent contamination, this tissue sample is called the explant.

2. The sample is sterilised by placing in ethanol or bleach.

3. The explant is placed in a sterile culture medium containing plant hormones (auxins etc.), this stimulates mitosis and the cells divide forming a mass called a callus.

4. The callus is divided up and individual cells or clumps from the callus are transferred to a new culture medium with different hormones and nutrients which stimulates the development of genetically identical plantlets.

5. These plantlets are transferred into compost where they can grow.

What is a tissue culture?

• Growing new tissues, organs or plants from certain tissues.

What are the advantages of micropropagation?

1. Allows for the rapid production of large numbers of plants with known genetic make-up which will yield good crops.

2. Culturing meristem tissue produces disease-free plants.

3. Provides a way of producing very large numbers of new plants which are seedless and therefore sterile to meet consumer tastes (like grapes and bananas).

4. Provides a way of reliably increasing the numbers of rare or endangered plants.

What are the limitations of micropropagation?

1. Produces a monoculture- many plants which are genetically identical, which means they are all susceptible to the same diseases or changes in growing conditions.

2. Relatively expensive and requires skilled workers.

3. Explants and plantlets are susceptible to mould while growing.

4. If source material is infected with a virus, all the clones will also be infected.

What is natural cloning in animals?

• In vertebrates it is less common but occurs in the form of twinning, where the early embryo splits into two.

• In invertebrates this can take several forms like fragmentation in starfish or hydra producing buds.

How does natural cloning occur in vertebrates?

• Occurs in the formation of monozygotic twins, the early embryo splits to form two separate embryos.

How does natural cloning occur in invertebrates?

• Starfish can regenerate entire animals from fragments of the original organism if they are damaged.

• Flatworms and sponges fragment and from new identical animals as part of their normal reproductive process, all clones of the original.

• Hydra produce buds which develop into genetically identical clones.

Why is it important that embryonic cells are totipotent?

• It has the potential to from an entire new animal.

What is artificial twinning?

• The process of producing monozygotic twins artificially.

What are the steps of artificial twinning?

1. Animal with desirable traits is treated with hormones, which release more mature ova than normal.

2. Ova may be fertilised artificially or naturally then the early embryos are taken carefully from the uterus, or they can be fertilised in a lab.

3. When the cells are still totipotent the cells of the embryo are split to produce several smaller embryos which are grown in the lab for a few days.

4. They are then each implanted into a surrogate mother, each implanted into a different mother to prevent risks.

5. They develop into foetuses and are born normally, a number of identical cloned animals are produced by different mothers.

What is somatic cell nuclear transfer (SCNT)?

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

What are the steps of SCNT?

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 the same species (is it 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 to term.

5. The new animal is a clone of the animal from which the original somatic cell is derived.

What are the arguments for animal cloning?

1. High-yielding farm animals that produce more offspring than normal reproduction.

2. Has the potential to enable rare, extinct or endangered animals to be reproduced.

3. Enables scientists to clone specific animals like race horses.

What are the arguments against animal cloning?

1. Very inefficient process- in many animals it takes many eggs to produce a single cloned offspring.

2. Many cloned animal embryos fail to develop and miscarry or produce malformed offspring.

3. Many animals have shortened lifespans.

4. Ethical issues.