6.3 Cloning

Question 1

Cloning definition

Answer 1

The process of producing genetically identical organisms, or sections of DNA which code for a specific trait

• Types of cloning: whole organism and gene cloning

Many organisms naturally produce clones through asexual reproduction, e.g. protists and bacteria

Question 2

Somatic cell nuclear transfer (SCNT)

Process of whole animal cloning

Answer 2

• Skin cells taken from adult being cloned are placed next to an ennucleated, unfertilised egg from an adult female
• Electric pulses are applied to cause the skin cell to fuse with the egg cell, creating an egg cell that has the genetic material of the skin cell
• The cell then divides into an early-stage embryo (blastocyst), which is implanted in a surrogate mother
• Dolly the Sheep was created this way, and this technique is also applied to plants

Question 3

Plant whole organism cloning

Answer 3

Vegetative propagation: aseuxal reproduction in plants where new plants are grown from parts of the parent plant, such as stems, roots, or leaves, instead of from seeds

Cutting:

• A cutting or clipping of a plant is grown elsewhere on its own, and after 1-3 weeks the roots will form a new organism identical to the original organism
• E.g. Succulents are grown using cuttings

Grafting:

• Part of a plant is cut (the cutting is called the scion) and grafted onto the root stock of another plant.
• The cuts are made with the same angles, so that over time the vascular bundles of the two plants can merge and the scion will become part of the root stock.
• The root stock allows the scion to access water and nutrients, so the scion grows into a clone of the original plant
• E.g. avocados

Tissue culture:

• Plant cells are taken from a part of the parent plant and grown in nutrient medium under controlled conditions
• The cells eventually form a callus, which is then cultured in a hormone-laden medium and develops into plantlets
  Plantlets can mature into fully grown plants when planted
• E.g. orchids

Question 4

Gene cloning

Answer 4

• A gene is selected and removed from the source DNA using restricton enzymes
• The gene is pasted into a vector DNA or plasmid through annealing and ligation
• The plasmid containing the gene is introduced into a host cell by the process of cell transformation
• Multiple copies fo the gene are created when the host cell reproduces

Question 5

Efficiency and ethics of cloning

Answer 5

Effectiveness:

• Cloning is currently ineffective
• Whole organism cloning typically has a low success rate: fewer than 10% of cloned animals survive to birth. The majority of losses are due to embryonic death, failure during implantation, or the development of a defective placenta

Ethical issues:

• Offspring of cloning are genetically the same age as the original organism it was cloned from, as the telomere of the DNA used to create the clone have been naturally shortened by biological aging. So the offspring are not born at age 0.
• This harms the organism: Dolly the Sheep should have lived to 11-12 years as other Finn-Dorset sheep, but she only lived to 6.5 years of age and had to be euthanised due to severe arthritis and progressive lung disease
• Can be unethical to the surrogate mother: if the surrogate is of another species, as is the case for the cloning of some extinct organisms, the surrogate may be harmed in carrying the pregnancy to term and birthing the offspring

Question 6

Assess the effectiveness of whole organisms and gene cloning

Answer 6

• Judgement
• Examples
• Effectiveness
• Ethics

Question 7

Celia the bucardo cloning

Cloning case study

Question 8

Whole organism cloning case study

Answer 8

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