6.4.3: Artificial clones in animals

Question 1

What is embryo twinning?

Answer 1

Splitting an embryo to create two genetically identical embryos.

Question 2

What is enucleation?

Answer 2

The removal of the cell nucleus.

Question 3

What is somatic cell nuclear transfer (SCNT)?

Answer 3

A technique that involves transferring the nucleus from a somatic cell to an egg cell.

Question 4

What are totipotent cells?

Answer 4

• Cells that can divide and differentiate into all types of cell found in the adult organism.
• In adults, the only truly totipotent cells are very early embryo cells.

Question 5

How could reproductive cloning be useful (what types od animals would we clone?

Answer 5

• Elite farm animals produced by selective breeding (artificial selection) or genetic modification can supply sperm for artificial insemination.
• Genetically modified animals with unusual characteristics, e.g. goats that produce spider silk in their milk and cows that produce less methane.

Question 6

Describe the steps in embryo splitting/twinning.

Answer 6

1. A zygote (fertilised egg) is created by IVF.
2. The zygote is allowed to divide by mitosis to form a small ball of cells.
3. The cells are separated and allowed to continue dividing.
4. Each small mass of cells is placed into the uterus of a surrogate mother

Question 7

What has embryo splitting been used for?

Answer 7

• Cloning elite farm animals

- Cloning animals for scientific research

Question 8

In embryo splitting, why is the precise phenotype of the animals unknown until they are born?

Answer 8

-The precise genotype and phenotype of the offspring produced will depend upon the sperm and egg used.

Question 9

What are the advantages of somatic cell nuclear transfer?

Answer 9

• Can be used to clone an adult.

- Therefore, the phenotype is known before cloning starts.

Question 10

When was SCNT first performed successfully on a mammal?

Answer 10

In 1996, to produce Dolly the sheep.

Question 11

Describe the steps in SCNT.

Answer 11

1. An egg cell is obtained and its nucleus is removed (enucleation)
2. A normal somatic cell (body cell) from the adult to be cloned is isolated and may have the nucleus removed.
3. The complete adult somatic cell or its nucleus is fused with the empty egg cell by applying an electric shock.
4. The shock also triggers the egg cell to start developing, as though it had just been fertilised.
5. The cell undergoes mitosis to produce a small ball of cells.
6. The young embryo is placed into the uterus of a surrogate mother.

Question 12

What is non-reproductive cloning?

Answer 12

The production of cloned cells and tissues for purposes other than reproduction.

Question 13

Give examples of how new tissues and organs can be grown as replacement parts for people who are not well:

Answer 13

• Skin can be grown in vitro to act as a graft over burned areas.
• Cloned cells have been used to repair damage to the spinal cord of a mouse and to restore the capability to produce insulin in the pancreas.
• Potential to grow whole new organs to replace diseased organs.

Question 14

Why could cloning avoid sole of the issues of organ transplants?

Answer 14

-Tissues grown from a patient’s own cells will be genetically identical and so avoid rejection, which is a problem when transplanting donated organs.

Question 15

How can cloning be used for scientific research?

Answer 15

• Genetically identical embryos can be used for scientific research into the action of genes that control development and differentiation.
• They can also be used to grow specific tissues or organs for use in tests on the effects of medicinal drugs.

Question 16

Pros and cons of cloning Individuals from an endangered species:

Answer 16

Pros:
-Individuals from an endangered species can be cloned to increase numbers.
Cons:
-This does not help to increase genetic diversity.

Question 17

Pros and cons of cloning animals to produce a whole herd of animals with desirable characteristics.

Answer 17

Pros:
-Can produce a whole herd with high yield or showing an unusual combination of characteristics (e.g. silk milk)
Cons:
-Lack of genetic diversity may expose the herd to certain diseases or pests.
-Animals may be produced with little regard for their welfare, which may have undesirable side effects such as meat-producing chickens that cannot walk.

Question 18

Pros and cons of cloning animals that are ‘high value’ individuals.

Answer 18

Pros:
-Produced genetically identical copies of high value individuals will retain the same characteristics.
Cons:
-The success rate of adult cell cloning is very poor.
-The method is a lot more expensive than conventional breeding.
-Cloned animals may be less healthy and have shorter life spans.

Question 19

Pros and cons of using genetically identical embryos and tissues for scientific research:

Answer 19

Pros:
-Allows the effects of genes and hormones to be assessed with no interference from different genotypes.
Cons:
-There are ethical issues regarding how long the embryo survives and whether it is right to create a life simply to destroy it.

Question 20

Why is testing medicinal drugs on cloned cells and tissues beneficial?

Answer 20

-Testing medicinal drugs on cloned cells and tissues avoids using animals or people for testing.