6.2.1 Cloning

What is cloning?

The process leading to the formation of a clone

What is meant by a clone?

A genetically identical copy of an organism

What are the advantages of cloning?

• Only need one parent

• Fast

• More efficient

• Same environment suitable for both parent and offspring

What are the disadvantages of cloning?

• Reduces genetic diversity

• No variation

• Smaller gene pool

• Organisms more vulnerable to environmental changes and disease

• More likely to pass down recessive alleles

• Selection is impossible

• Could lead to overcrowding which increases competition

What process does natural cloning in plants involve?

Vegetative propagation

What is vegetative propagation?

Process of reproduction through the vegetative parts of the plant (rather than through reproductive structures)

Give 7 types of natural cloning in plants

1. Tubers

2. Leaves

3. Bulbs

4. Corms

5. Runners

6. Suckers

7. Rhizomes

Describe the process of natural cloning in tubers

• Type of underground stem

• e.g. potatoes

• Tuber grows into one or more plants

• These then go on to produce many new tubers

Describe the process of natural cloning in leaves

• Clones grow on leaf margins

• These drop off the leaf and take root

Describe the process of natural cloning in bulbs

• Type of fleshy underground stem with fleshy leaf bases

• e.g. onions

• Over-wintering mechanism

• Contains one or more apical buds

• Each of these apical buds grow into a new plant in the spring

Describe the process of natural cloning in corms

• Type of solid underground stem with scaly leaves and buds

• Over-wintering mechanism

• Remain in the ground over winter

• The buds form new plants in the spring

Describe the process of natural cloning in runners

• Plant have horizontal stems (called runners) that form over the soil surface

• Root forms under nodes of runners

• Runner dies when the plant can survive by itself

• E.g. strawberry plants

Describe the process of natural cloning in suckers

• Plant has a horizontal stem (sucker) that grows from the root of many trees and shrubs

• The sucker dies and the new stem grows as a separate organism

• E.g. cherries

Describe the process of natural cloning in rhizomes

• Plant has a horizontal stem (rhizome) that grows horizontally underground

• The rhizome dies and the new stem grows as a separate organism

• E.g. ginger

What are the advantages of vegetative propagation in agriculture?

• Some plants cannot reproduce sexually

• Quicker than growing from seed/ sexual reproduction

• Produces uniform yield with predictable quality

• Easier to harvest

• Can be done at any time of year

What are methods of artificial cloning in plants?

• Tissue culture AKA micropropagation

• Cuttings

What are different types of cuttings?

• Root cuttings

• stem cuttings

• leaf cuttings

• scion cuttings (dormant woody twigs)

How are plant cuttings used as a cloning technique?

1. Use a healthy shoot cut from a healthy plant

2. Cut stem at a slant between nodes

3. Dip in rooting powder. Rooting powder contains auxin which promotes mitosis and cell differentiation

4. Roots grow

5. Cutting placed into soil

6. Cover with plastic bag to reduce transpiration

What is tissue culture or micropropagation

Series of techniques used to grow new tissues, organs or plants from certain tissues cut from a sample plant

Why is tissue culture/ micropropagation only possible for plants and not for animals?

• many plants cells are totipotent, unlike animal cells

• So an entire plant can be reproduced from any of these cells

Describe the process of micropropagation/ tissue culture

1. A sterile environment should be used to prevent contamination of fungi or bacteria

2. Cut the plant into small pieces, called explants

3. Sterilise explants using dilute bleach or alcohol

4. Place explants in sterile growth medium. This contains suitable nutrients and plant growth substances needed e.g. auxin and cytokinin

5. This stimulates the cells of each explant to divide by mitosis to form a callus (mass of undifferentiated totipotent cells)

6. Grow different clumps in different growth media so they differentiate into different plant tissues

7. Transfer tiny plants to a greenhouse to allow it to grow further

What are the advantages of artificial cloning in plants?

• Offspring has same desirable characteristic

• Fast

• Can be carried out where sexual reproduction is not possible

• Grow plants that are hard to grow from seeds

What are the disadvantages of artificial cloning in plants?

• Tissue culture is labour intensive

• Expensive to set up facilities

• Susceptible to same pests and diseases

• Can lead to rapid spread of disease as no genetic variation

Compare the equipment and techniques of taking cuttings with those used for micropropagation

• Micropropagation needs more equipment

• Micropropagation needs more skills

• Micropropagation produces more clone offspring

What are examples of natural cloning in animals?

• Identical twins

• Some small animals that reproduce asexually e.g. aphids

How are identical twins formed?

• Egg is fertilised by sperm

• Forms a zygote

• Zygote undergoes a few mitotic divisions to form an embryo

• Embryo splits in two to form two identical embryos

• These grow to result in the birth of two identical offspring

What are three methods of artificial cloning in animals?

• Artificial embryo twinning (reproductive cloning)

• Somatic cell nuclear transfer (SCNT) (reproductive cloning)

• Therapeutic cloning (non-reproductive cloning)

How does embryo twinning produce artificial clones?

• Embryo is divided into two half embryos

• These are inserted into a surrogate mother

• The surrogate mother gives birth to identical twins

How does somatic cell nuclear transfer (SCNT) produce artificial clones?

• Animal to be cloned donates a somatic (body) cell

• The egg cell is extracted from the egg donor and enucleated (nucleus is removed and discarded)

• The nucleus from the somatic cell is injected into the enucleated egg cell

• The hybrid zygote cell is treated to encourage it to divide by mitosis

• The embryo is implanted into the surrogate mother for gestation and birth

What is an example of SCNT being used?

Dolly the sheep

What is the use of therapeutic cloning?

Clone cells to replace dead or damaged cells that cause a loss of function in an individual

How does therapeutic cloning produce artificial clones?

• Embryos are cloned as in reproductive cloning

• Embryos are removed and subdivided

• Each embryo cell is a totipotent stem cell that can be cultured and artificially differentiated into any type of specialised cell

What are some examples of conditions that therapeutic cloning can be used to treat?

• Parkinson’s Disease

• Diabetes

• Grow organs for organ transplants (so no rejection)

What are some uses of reproductive cloning?

• Livestock farming

• Clone animals with desirable characteristics for maximising agricultural output

• Help preserve endangered species

• Remove less desirable characteristics from the gene pool over time

What are some arguments for artificial cloning in animals?

• Produces many animals with desirable characteristics

• Produces many animals with unusual combinations of characteristics

• Clone individuals from endangered species to increase yield

• Use to research effects of genes and hormones

• Use to test medicinal drugs, so don’t need to test on animals or people

• Used in repairing damage caused by disease or accidents

What are some arguments against artificial cloning in animals?

• Lack of genetic variation

• Increases risk of whole herd to diseases and pests

• Doesn’t increase genetic diversity

• Animals produced with little regard for their welfare

• Poor success rate of adult cell cloning

• Adult cell cloning is expensive

• Cloned animals may be less healthy and have shorter life spans

• Ethical issues surrounding embryo use in research: is it right to create life simply to destroy it?